Update the Handler.gs file on the func HandlerPlayerUpdate section. Normally, the scuba is checked on the set costume coding so that if Dizzy is wearing the scuba that tile is used rather than the standard tiles. You can amend this to reflect the new set of tiles , such as using the status of a hidden dynamic object to amend the costume, ie:
if (ObjGet(ObjFind(1000), O_STATUS) == 2) costume+=300 (or whatever starting tile number of the different set of tiles are - you may have to add ten to the file numbers to get the engine to opt for the right file, ie could be 310.
Change the status when you pick up or drop whatever item you are showing on the new set of tiles.
I'd recommend making a copy of the original Handler. gs file, so that you can replace it and start again if you totally screw up the coding.
I would offer you check out some of my games where this happens, such as Daisy's quest (wearing different coloured glasses), but typically, I think I password protected the pak file and have forgotten the password to unpack it. Sorry.