Changing Default Playermodels for a Map

Hello, I have an idea to put a custom default playermodel in for certain maps. It would have it so the default playermodel is changed to a custom playermodel for that map only (eg, a pirate playermodel for a pirate map). Does anyone know how I would go about doing this on already made maps?

Also if anyone knows of a way to do this that allows random selection of certain playermodels that would awesome.