I saw pokeguy changing date to get a Drilbur. If changing date glitch is allowed, can we send pokemons to farm Exp?

I'm pretty sure that is tied to actual time and wouldn't work.

But basically yes, every single glitch is allowed until some crazy glitch will be found that would skip so much and force to make a glitchless category

It's fully possible to finish pokejobs with the glitch. It's just slow because you have to run to a PC. Maybe it'd be good after a few gyms when you can train a full party.

Just simply changing the clock within the system settings isn't a glitch. Although, the game does have a punishment system for doing that, and bypassing that could be considered a glitch (changing the clock when you are in the "Invite Others" screen bypasses it, and even then it is debatable whether that glitch would be prohibited under the "No usage of Communication Features" rule, since the glitch seems to rely on the game attempting to communicate to other Switches. This glitch might just get patched out anyways, so that might just make this a moot point, assuming Mods don't just do some category split or just allow any 1.0 exclusive glitches). Weather changes aren't covered under the punishment system so there isn't a need to use that glitch.

Also, I'm pretty sure Any% is meant to be Glitchless anyways, judging from what I see from the Discord server, although I might be wrong about that.

Rules specify nothing about glitches. I doubt they're banned from Any%. The thing is that they're not used until now as the applications of the glitches found so far are either inconsistent or generally slower. Hence it's not used right now.