Keep the custom messages set for each level under Membership >> Membership Levels and combine it with the PMPro Approvals status.

custom-level-confirmation-message-for-pmpro-approvals.php

<?php
/**
 * Create a custom confirmation for Approvals Add On.
 *
 * 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/
 */

function modify_status_from_confirmation_message( $confirmation_message, $pmpro_invoice ) {

	// Bail if necessary
	if ( ! class_exists( 'PMPro_Approvals' ) ) {
		return $confirmation_message;
	}

	global $current_user, $wpdb;

	$approval_status = null;
	$approval_status = PMPro_Approvals::getUserApprovalStatus();

	$users_level = pmpro_getMembershipLevelForUser( $current_user->ID );
	$level_id    = $users_level->ID;

	//if current level does not require approval keep confirmation message the same.
	if ( ! PMPro_Approvals::requiresApproval( $level_id ) ) {
		return $confirmation_message;
	}

	if ( ! empty( $approval_status ) ) {
		$confirmation_message = '<p>' . sprintf( __( 'Thank you for your membership to %1$s. Your %2$s membership status is: <b>%3$s</b>.', 'pmpro-approvals' ), get_bloginfo( 'name' ), $current_user->membership_level->name, $approval_status ) . '</p>';
	}

	$level_message = $wpdb->get_var( $wpdb->prepare( "SELECT l.confirmation FROM $wpdb->pmpro_membership_levels l LEFT JOIN $wpdb->pmpro_memberships_users mu ON l.id = mu.membership_id WHERE mu.status = 'active' AND mu.user_id = %d LIMIT 1", $current_user->ID ) );
	if ( ! empty( $level_message ) ) {
		$confirmation_message .= "\n" . stripslashes( $level_message ) . "\n";
	}
	$confirmation_message .= '<p>' . __( 'Below are details about your membership account:' ) . '</p>';

	return $confirmation_message;
}

function my_pmpro_approvals_change_approval_confirmation_hook() {

	// Swop only if Approvals is active and custom function exist.
	if ( class_exists( 'PMPro_Approvals' ) && function_exists( 'modify_status_from_confirmation_message' ) ) {
		remove_filter( 'pmpro_confirmation_message', array( 'PMPro_Approvals', 'pmpro_confirmation_message' ) );
		add_filter( 'pmpro_confirmation_message', 'modify_status_from_confirmation_message', 10, 2 );
	}
}

add_action( 'init', 'my_pmpro_approvals_change_approval_confirmation_hook' );

This is an edited copy of https://gist.github.com/greathmaster/e222c6fd11a3a077c955d02f56463164