On Forms, alerts are part of the form. You can customize them and make your own.
declare btn_id as integer
on some action (like when a button is pressed):
change_alert_message('alert_type','Your alert message.');
btn_id := show_alert('alert_type');
IF-THEN-ELSE code under this to handle the action (button selected) by the user.
triggers are always an option, though I would caution that you be aware of what it may or may not do to your app's upgrade path. Use a naming convention that separates your triggers from delivered triggers, and I recommend against altering delivered triggers unless it's absolutely necessary and documented to the teeth.
edit - that is, if you're hammering on an app that was developed by someone else. If yer developing it nevermind