Ab test say 20 creative in an adset and let Facebook find the best creative for you in a cbo. Once set it is set and best not to change the creative just launch a new ad set with the new creative. You can change it but not ideal or how you should run Facebook ads with a proper account structure to maintain data transparency. Also with Facebook algo suspending and disabling ad accounts like crazy swapping creative after approved looks very fishy and can trigger negativr signals.