So I want to get back into running this game again. I was watching TGH's WR run to learn what I'm doing wrong, and in the video currently up, he mentioned something about we are allowed to pre make a save so we don't have to keep doing the RNG manip everytime we reset..

I just wanna double confirm that this IS allowed, and I won't get a rejected run if I use this method.

That's right. You can start from a pre made file now to avoid having to manip the egg pattern every time. You do still have to include launching the game from the Switch Home screen in the recording though.

I've always been curious about that. Why? Does it have to do with seeing if it is an emulator or not? That's the only thing I can think of.

I believe it had something to do with some load screens being stored in memory for digital versions so they would load faster without a full game close and reopen. This would give some amount of unfair advantage. Im sure theres more to it though.

It's to avoid preloading. The game keeps assets in memory so load times get shorter if you don't completely close the game between runs.