Don't apply set expiration date if renewing.

my_pmpro_checkout_level.php

<?php

// Don't apply set expiration date if renewing.
function my_pmpro_checkout_level( $checkout_level ) {
    // Get current level.
    $user_level = pmpro_getMembershipLevelForUser();
    if ( ! empty( $user_level ) && $user_level->id == $checkout_level->id ) {
        // Remove Set Expiration Date filters.
        remove_filter("pmpro_checkout_level", "pmprosed_pmpro_checkout_level");
        remove_filter('pmpro_discount_code_level', 'pmprosed_pmpro_checkout_level', 10, 2);
        remove_filter('pmpro_ipnhandler_level', 'pmprosed_pmpro_checkout_level');
    }
    
    return $checkout_level;
}
add_filter( 'pmpro_checkout_level', 'my_pmpro_checkout_level', 5 );

function my_pmpro_level_expiration_text( $text, $checkout_level ) {
    // Get current level.
    $user_level = pmpro_getMembershipLevelForUser();
    if ( ! empty( $user_level ) && $user_level->id == $checkout_level->id ) {
        // Remove Set Expiration Date filters.
        remove_filter('pmpro_level_expiration_text', 'pmprosed_pmpro_level_expiration_text', 10, 2);
    }
}
add_filter( 'pmpro_level_expiration_text', 'my_pmpro_level_expiration_text', 5, 2 );