You can create a custom priority selector with a custom field.
To customize your card fields, go to Settings - Card Template. Enable a custom field, by checking Custom field 1 and changing the label to, e.g., Priority, then select the Dropdown with options type and set your custom priority values, e.g., top priority, urgent, high, normal, low.
Notably, a custom priority field set up like this will not generate standard priority icons on the fronts of your cards.