I guess I could use SNEEK/UNEEK and have SSBB as a folder where I can just replace the audio/texture files.
Go ahead and try it. It won't work. Riivolution won't ever get to the point of it launching a game because *neek patches every IOS so riivolution will want to download a new IOS37, but that will be patched also.... so you won't get very far.
I think it will might work depending on the package. It worked for me for fatal frame 4 (loaded using cfg but *neek should work too).
As long as only files are replaced it should work for other packages too.
If it does in memory patching that will have to be converted to a cheat instead. Might be hard to do but should be possible.
Indeed. If it is just file replacement that is needed, then all that you would need to do, chaosdarkneo, is to setup xNEEK+DI (ModMii can help you with this if you have not setup xNEEK+DI before), and then use the DiscEx tool to convert/extract a SMG2 .iso to "DiscEx" format, which is pretty much just a folder with all of the games extracted files in it. AFAIK (I have not actually used "DiscEx" format myself to actually test this), since it is now just a directory with all the extracted files, just copying and pasting to replace the original files with modified ones should work. Copying files over after you modify them every time might not be as convenient as using Riivolution and RiiFS, but it still does the job, at least until you get yourself a new SMG2 disc.
And the same should also be applicable for SSBB, the_randomizer. (AFAIK as long as it is just file replacement)