Reposition a Middle Name User Field between the First Name and Last Name fields from the Add Name to Checkout Add On.

my_pmproan2c_middle_name_user_field.php

<?php
/**
 * Reposition a Middle Name User Field between the First Name and Last Name
 * fields from the Add Name to Checkout Add On.
 *
 * Note: The field's name must be middle_name, label can be something else.
 *
 * You can add this recipe to your site by creating a custom plugin
 * or using the Code Snippets plugin available for free in the WordPress repository.
 * Read this companion article for step-by-step directions on either method.
 * https://www.paidmembershipspro.com/create-a-plugin-for-pmpro-customizations/
 */

/**
 * Move field on checkout page.
 */
function my_pmproan2c_checkout_move_middle_name_user_field() {
	// Bail if Add Name to Checkout Add On isn't active.
    if ( ! function_exists( 'pmproan2c_pmpro_checkout_after_password' ) ) {
        return;
    }

	// Bail if PMPro isn't active, or not on checkout page.
	if ( ! function_exists( 'pmpro_is_checkout' ) || ! pmpro_is_checkout() ) {
		return;
	}
	?>
	<script>
	document.addEventListener('DOMContentLoaded', function () {
		const middleNameDiv = document.getElementById('middle_name_div');
		const an2cDiv = document.getElementById('pmpro_an2c');
		const firstNameField = document.querySelector('.pmpro_form_field-firstname');

		if (middleNameDiv && an2cDiv) {
			an2cDiv.classList.replace('pmpro_cols-2', 'pmpro_cols-3');
		}

		if (middleNameDiv && firstNameField) {
			firstNameField.insertAdjacentElement('afterend', middleNameDiv);
		}
	});
	</script>
	<?php
}
add_action( 'wp_footer', 'my_pmproan2c_checkout_move_middle_name_user_field' );

/**
 * Move field on Member Profile Edit page.
 */
function my_pmproan2c_profile_edit_move_middle_name_user_field() {
	global $pmpro_pages, $post;
	
	// Bail if PMPro isn't active or Add Name to Checkout Add On isn't active.
	if ( ! function_exists( 'pmpro_is_checkout' ) || ! function_exists( 'pmproan2c_pmpro_checkout_after_password' ) ) {
		return;
	}

	// Bail if we're not on the PMPro Member Profile Edit page.
	if ( empty( $pmpro_pages['member_profile_edit'] ) || ! is_page( $pmpro_pages['member_profile_edit'] ) ) {
		return;
	}
	?>
	<script>
	document.addEventListener('DOMContentLoaded', function () {
		const accountInfo = document.getElementById('pmpro_member_profile_edit-account-information');
		const middleNameDiv = document.getElementById('middle_name_div');
		const firstNameField = accountInfo ? accountInfo.querySelector('.pmpro_form_field-first_name') : null;
		const colsDiv = accountInfo ? accountInfo.querySelector('.pmpro_cols-2') : null;

		if (accountInfo && firstNameField && middleNameDiv && colsDiv) {
			colsDiv.classList.replace('pmpro_cols-2', 'pmpro_cols-3');
			firstNameField.insertAdjacentElement('afterend', middleNameDiv);
		}
	});
	</script>
	<?php
}
add_action( 'wp_footer', 'my_pmproan2c_profile_edit_move_middle_name_user_field' );