You can do that using adverts_register_taxonomy and wpadverts_mal_register_taxonomy filters
add_action("adverts_register_taxonomy", "customize_adverts_taxonomy", 10, 2 );
function customize_adverts_taxonomy( $args, $type = null ) {
if( $type != "advert_category" ) {
return $args;
}
if(!isset($args["rewrite"])) {
$args["rewrite"] = array();
}
$args["rewrite"]["slug"] = "ad-category";
return $args;
}
add_action("wpadverts_mal_register_taxonomy", "customize_location_taxonomy", 10, 2 );
function customize_location_taxonomy( $args, $type = null ) {
if( $type != "advert_location" ) {
return $args;
}
if(!isset($args["rewrite"])) {
$args["rewrite"] = array();
}
$args["rewrite"]["slug"] = "ad-location";
return $args;
}
See https://github.com/simpliko/wpadverts-snippets/blob/master/custom-slugs/custom-slugs.php for more details.