Allows renewing yearly memberships with a set expiration date. Requires the Set Expiration Dates Add On for Paid Memberships Pro

customization.php

/*
	Allows renewing yearly memberships with a set expiration date.
	E.g. if the level expires on 1/1/2020 and the member renews their membership before then, their membership will be extended to 1/1/2021
	Requires the Set Expiration Dates Add On for Paid Memberships Pro
*/
function my_pmpro_yearly_membership_renewal($level) {

	$extend_level = 1; //change to the level with a set expiration date

	if( $level->id == $extend_level && pmpro_hasMembershipLevel( $extend_level ) ) 
	{
		global $wpdb;
		$user_id = get_current_user_id();
		$sqlQuery = "SELECT enddate FROM $wpdb->pmpro_memberships_users WHERE user_id = '" . esc_sql( $user_id ) . "' AND membership_id = '" . esc_sql( $level->id ) . "' AND status = 'active' ORDER BY id DESC LIMIT 1";
		$old_enddate = $wpdb->get_var( $sqlQuery );
		$endyear = intval( substr( $old_enddate, 0, 4 ) ) + 1;
		$new_endtime = $endyear . substr( $old_enddate, 4 );
		$new_enddate = strtotime( $new_endtime );
		$today = new DateTime();
		$new_expiration_date = date_create();
		date_timestamp_set( $new_expiration_date, $new_enddate );
		// Compute and apply the difference
		$difference = $new_expiration_date->diff( $today );
		$level->expiration_number = $difference->days + 1;
		$level->expiration_period = 'Days';
	}
	return $level;
}
add_filter('pmpro_checkout_level', 'my_pmpro_yearly_membership_renewal', 20, 1);

function my_pmpro_yearly_membership_renewal_text( $expiration_text, $level) {

	$extend_level = 1; //change to the level with a set expiration date

	if( $level->id == $extend_level && pmpro_hasMembershipLevel( $extend_level ) )
	{
		$enddate = date( get_option('date_format'), strtotime( "+$level->expiration_number days" ) );
		$expiration_text = "Membership expires on $enddate.";
	}
	return $expiration_text;
}

add_filter( 'pmpro_level_expiration_text', 'my_pmpro_yearly_membership_renewal_text', 20, 2 );