wpcm-change-slug.php

// WP Car Manager change slug - Add this to your theme's functions.php
function wpcm_change_slug( $translated, $text, $context, $domain ) {
	if ( 'wp-car-manager' == $domain ) {
		if ( 'vehicle' == $text && 'post type slug' == $context ) {
			$translated = 'my-cars';  // change slug of vehicle
		}
	}

	return $translated;
}
add_filter( 'gettext_with_context', 'wpcm_change_slug', 10, 4 );