Customize the teaser text (typically set in the advanced options) using filters with Paid Memberships Pro.

pmpro_custom_teaser_text.php

/*
  Edit Teaser Messages Depending on Content
  
  In the example below, we have 3 levels with IDs 1, 2, and 3. Level 1 is a free level.
  Level 2 is a paid level. Level 3 is a higher-tiered paid level.
  
  So each level is an upgrade over the other. All level 2 members have access to level 1 content, etc.
  
  When showing teaser text, we check if the current post is available to free members.
  If so, we show a link to register for the free level. If not, we show a link to the paid level.
  
  Change the level IDs, logic, and text to fit your needs. Then paste this into your active theme's functions.php
  or a custom plugin.
*/

//for not logged in users
function pmpro_pmpro_not_logged_in_text_filter($text)
{
	global $post;
	
	$access = pmpro_has_membership_access($post->ID, NULL, true);
	$level_ids = $access[1];
		
	if(is_array($level_ids) && in_array(1, $level_ids))
	{
		$text = '
			This page is restricted to Free level members or higher.<br /><br />
			<strong>Already have an account? <a href="/login?redirect_to=' . urlencode($_SERVER['REQUEST_URI']) . '">Login Now »</a></strong>
			<strong>New to this site? <a href="/membership-checkout/?level=1">Register Now »</a></strong>
			';
	}
	else
	{
		$text = '
			This page is restricted to PMPro level members or higher.<br /><br />
			<strong>Already have an account? <a href="/login?redirect_to=' . urlencode($_SERVER['REQUEST_URI']) . '">Login Now »</a></strong>
			<strong>New to this site? <a href="/membership-checkout/?level=2">Register Now »</a></strong>
			';
	}

	return $text;
}
add_filter("pmpro_not_logged_in_text_filter", "pmpro_pmpro_not_logged_in_text_filter");

//for logged-in non-members
function pmpro_pmpro_non_member_text_filter($text)
{
	global $post;
	
	$access = pmpro_has_membership_access($post->ID, NULL, true);
	$level_ids = $access[1];
		
	if(is_array($level_ids) && in_array(1, $level_ids))
	{
		$text = '
			This page is restricted to Free level members or higher. <a href="/membership-checkout/?level=1">Upgrade Now »</a></strong>
			';
	}
	else
	{
		$text = '
			This page is restricted to PMPro level members or higher. <a href="/membership-checkout/?level=2">Upgrade Now »</a></strong>
			';
	}

	return $text;
}
add_filter("pmpro_non_member_text_filter", "pmpro_pmpro_non_member_text_filter");