I'm reviving my old as nails account just to post on this thread, because this is coincidentally something I've been looking into lately.
From my tests, the retail release of Pizza Tower runs totally fine without Fmod; just without audio as you'd probably be able to guess. Earlier releases didn't rely on Fmod for sound, so I suppose in theory it'd be possible to write an audio implementation that doesn't rely on a plug in, but I can't imagine many people being interested in that undertaking.
The real issue with doing a Pizza Tower asset swap is that the GMS version is unsupported by Yoyoloader, to my knowledge. I did attempt doing it with the closest approximation I could find in the compatibility sheet, to no avail.
An interesting workaround to this would be compiling a native version of Pizza Tower for Android, since the source files for the final release have been leaked (which I won't be sharing here for obvious reasons, since it's copyrighted material). While I've been unable to get a cracked version of GM2 set up to compile it myself, someone /has/ managed to put a working .apk version of the game.
Sadly I have not been able to run that apk on YoYoLoader, since I end up getting some arcane error that doesn't appear to be well documented. It's been a hot minute since I tried, but if there's enough interest I can hop back into my Vita and get the exact error code to see if something can be done about it.