Referring to this post on github:https://github.com/danahutchins/wp-members-bootstrap-forms/blob/master/wp-members-pluggable.php

wpmem_bootstrap_filters.php

<?php
/**
 * This gist is set up to diplay the correct way to customize forms in WP-Members.
 * 
 * It is in reference to this script file:
 * https://github.com/danahutchins/wp-members-bootstrap-forms/blob/master/wp-members-pluggable.php
 * 
 * The author of that script indicates in this post: 
 * http://www.inforest.com/updating-wp-members-wordpress-plugin-for-twitter-bootstrap/
 * that "Rather than going to the trouble of writing hooks, I decided to simply 
 * write new functions to generate the forms for Bootstrap, because it was easier 
 * and I assumed any changes to these functions would probably require rewriting 
 * hooks anyway."
 * 
 * While I applaud Dana's efforts as well as his sharing this in general, 
 * that's actually not a good approach. That is why I am posting this as I would
 * like to discourage that approach while explaining why and giving what is the
 * preferred approach.
 * 
 * First, you would not go to the trouble of "writing hooks" - the hooks 
 * are already there.  What you would go through the trouble of would be hooking
 * filter functions to those hooks.  If you're going to bother to rewrite the 
 * function, it would in fact be much easier to use thefilters AND you would 
 * end up with a result that would not require you to rewrite your work when 
 * you update, as Dana assumed.
 * 
 * Pluggable functions should only be used as a last resort when there is no 
 * current way to implement a necessary feature or customization.  The trade-off 
 * with pluggable functions is that they may not be compatible with future 
 * releases, as will be the case with the above mentioned implementation when 
 * version 3.1 is released.  If done correctly using the appropriate filter
 * hooks, the result would be fully compatible when updating.
 * 
 * These filters currently cover everything in the above mentioned post except
 * the registration form function.
 */

add_filter( 'wpmem_restricted_msg', 'my_restricted_msg' );
function my_restricted_msg( $str ) {
	return '<h4>Sell Sheets  |  Art Files  |  Order Forms</h4>';
}

/**
 * Since the login and password change/reset forms need
 * the same custom classes, the same function can be used
 * for all three of these filters.
 */
add_filter( 'wpmem_inc_login_inputs',          'my_custom_inputs' );
add_filter( 'wpmem_inc_changepassword_inputs', 'my_custom_inputs' );
add_filter( 'wpmem_inc_resetpassword_inputs',  'my_custom_inputs' );
function my_custom_inputs( $default_inputs ) {
	$default_inputs[0]['class'] = 'form-control';
	$default_inputs[0]['div']   = 'col-sm-8';
	$default_inputs[1]['class'] = 'form-control';
	$default_inputs[1]['div']   = 'col-sm-8';
	return $default_inputs;
}

add_filter( 'wpmem_inc_login_args', 'my_inc_login_args' );
function my_inc_login_args( $args ) {
	$args['heading'] = 'Established Users';
	return $args;
}

/**
 * This filter actually handles the login form, the password reset form,
 * the change password form, and the new forgot username form.
 */
add_filter( 'wpmem_login_form', 'my_login_form', 10, 2 );
function my_login_form( $form, $toggle ) {
	global $wpmem;
	// Put the custom opening div wrappers before original form HTML
	$form = "<div class=\"row grey\"><div class=\"col-sm-6 grey\">" . $form;
	// Continue with custom HTML that comes after the form HTML.
	$form .= "</div>\n";
	$form .= "<div class=\"col-sm-6\">";
	$form .= "<h3>New Users</h3>\n";
	$form .= "<p>If you are a Dutch Cheese Maker broker or customer and would like to apply for access, click \"Create Account\" and enter the information requested on the next page.</p>\n";
	$form .= '<div style="text-align:center;"><a class="btn btn-primary contact-btn" href="' . $wpmem->user_pages['register'] . '">Create Account</a></div>';
	$form .= "</div>\n";
	$form .= "</div>\n";

	return $form;
}

/**
 * This filter actually handles the login form, the password reset form,
 * the change password form, and the new forgot username form.
 */
add_filter( 'wpmem_login_form_args', 'my_login_form_args', 10, 2 );
function my_login_form_args( $args, $action ) {
	$args = array( 
		'heading_before'  => '<h3>',
		'heading_after'   => '</h3>',
		'fieldset_before' => '<div class="form-group">',
		'fieldset_after'  => '</div>',
		'buttons_before'  => '<div class="form-group"><div class="col-sm-offset-4 col-sm-8">',
		'buttons_after'   => '</div></div>',
		'link_before'     => '<div class="row"><div class="col-sm-offset-2 col-sm-10">',
		'link_after'      => '</div></div>',
		'form_class'      => 'form-horizontal',
		'button_class'    => 'btn btn-primary contact-btn',
	);

	return $args;
}

/**
 * This filter actually handles the login form, the password reset form,
 * the change password form, and the new forgot username form.
 */
add_filter( 'wpmem_login_form_rows', 'my_login_form_rows', 10, 2 );
function my_login_form_rows( $rows, $action ) {
	// Set up replacement variables.
	$old = '<label';
	$new = '<label class="col-sm-4 control-label" ';
	// str_replace on the label tag to slip in custom class.
	$rows[0]['label'] = str_replace( $old, $new, $rows[0]['label'] );
	$rows[1]['label'] = str_replace( $old, $new, $rows[1]['label'] );
	
	return $rows;
}

wpmem_inc_login_args.php

<?php // ignore this line

/**
 * This filters the heading instead of changing it in the
 * pluggable version at line 78.
 */
add_filter( 'wpmem_inc_login_args', 'my_inc_login_args' );
function my_inc_login_args( $args ) {
	$args['heading'] = 'Established Users';
	return $args;
}

wpmem_inc_login_inputs.php

<?php // ignore this line

/**
 * Since the login and password change/reset forms need
 * the same custom classes, the same function can be used
 * for all three of these filters.
 * 
 * Note: these are classes that in the pluggable version were set
 * by changing the class and div values at lines 56 & 57.
 */
add_filter( 'wpmem_inc_login_inputs',          'my_custom_inputs' );
add_filter( 'wpmem_inc_changepassword_inputs', 'my_custom_inputs' );
add_filter( 'wpmem_inc_resetpassword_inputs',  'my_custom_inputs' );
function my_custom_inputs( $default_inputs ) {
	$default_inputs[0]['class'] = 'form-control';
	$default_inputs[0]['div']   = 'col-sm-8';
	$default_inputs[1]['class'] = 'form-control';
	$default_inputs[1]['div']   = 'col-sm-8';
	return $default_inputs;
}

wpmem_login_form.php

<?php // ignore this line

/**
 * This filter actually handles the login form, the password reset form,
 * the change password form, and the new forgot username form.
 * 
 * This makes the changes that are done in the pluggable version 
 * at lines 96-107
 */
add_filter( 'wpmem_login_form', 'my_login_form', 10, 2 );
function my_login_form( $form, $toggle ) {
	global $wpmem;
	// Put the custom opening div wrappers before original form HTML
	$form = "<div class=\"row grey\"><div class=\"col-sm-6 grey\">" . $form;
	// Continue with custom HTML that comes after the form HTML.
	$form .= "</div>\n";
	$form .= "<div class=\"col-sm-6\">";
	$form .= "<h3>New Users</h3>\n";
	$form .= "<p>If you are a Dutch Cheese Maker broker or customer and would like to apply for access, click \"Create Account\" and enter the information requested on the next page.</p>\n";
	$form .= '<div style="text-align:center;"><a class="btn btn-primary contact-btn" href="' . $wpmem->user_pages['register'] . '">Create Account</a></div>';
	$form .= "</div>\n";
	$form .= "</div>\n";

	return $form;
}

wpmem_login_form_args.php

<?php // ignore this line

/**
 * This filter actually handles the login form, the password reset form,
 * the change password form, and the new forgot username form.
 * 
 * This changes the general HTML that the pluggable version changes by
 * editing the default in line 129-157
 */
add_filter( 'wpmem_login_form_args', 'my_login_form_args', 10, 2 );
function my_login_form_args( $args, $action ) {
	$args = array( 
		'heading_before'  => '<h3>',
		'heading_after'   => '</h3>',
		'fieldset_before' => '<div class="form-group">',
		'fieldset_after'  => '</div>',
		'buttons_before'  => '<div class="form-group"><div class="col-sm-offset-4 col-sm-8">',
		'buttons_after'   => '</div></div>',
		'link_before'     => '<div class="row"><div class="col-sm-offset-2 col-sm-10">',
		'link_after'      => '</div></div>',
		'form_class'      => 'form-horizontal',
		'button_class'    => 'btn btn-primary contact-btn',
	);

	return $args;
}

wpmem_login_form_rows.php

<?php // ignore this line

/**
 * This filter actually handles the login form, the password reset form,
 * the change password form, and the new forgot username form.
 * 
 * This makes the change to the label tag that the pluggable version 
 * changes at line 179.
 * 
 * This is the one tricky piece of the process because there isn't
 * currently a direct process of adding/changing a class in the 
 * label tag itself (at least in the login form), so you must use
 * the php str_replace function to do a find/replace (that's the 
 * $old/$new part).
 */
add_filter( 'wpmem_login_form_rows', 'my_login_form_rows', 10, 2 );
function my_login_form_rows( $rows, $action ) {
	// Set up replacement variables.
	$old = '<label';
	$new = '<label class="col-sm-4 control-label" ';
	// str_replace on the label tag to slip in custom class.
	$rows[0]['label'] = str_replace( $old, $new, $rows[0]['label'] );
	$rows[1]['label'] = str_replace( $old, $new, $rows[1]['label'] );
	
	return $rows;
}

wpmem_restricted_msg.php

<?php // ignore this line

/**
 * This handles the change at line 35 in wp-members-pluggable.php
 * 
 * Note that the original script then comments out the filter application
 * at line 45, nullifying the wpmem_restricted_msg filter.
 */
add_filter( 'wpmem_restricted_msg', 'my_restricted_msg' );
function my_restricted_msg( $str ) {
	return '<h4>Sell Sheets  |  Art Files  |  Order Forms</h4>';
}