Found a site with a thread based entirely on Super Mario Sunshine cheats/hacks.

board.gscentral.org/retro-hacking/17697.htm

Haven't gone through the entire the thread yet myself (only 42 posts in; 200+ posts in thread and counting) but maybe, just maybe, somebody here will find a use for these (cause it sure won't be me).

EDIT (IMPORTANT): From what I've read, most of this stuff, if not all of it, is for the PAL version. I think.

Meanwhile, Summer Break begins for me in only a few weeks, so hopefully I'll be more active then and be able to search the game for more goodies of sorts.