I'm emulating Emerald, and I want to be able to acquire Pokémon otherwise only obtainable through trading. What application/s would I use, and what would I do in such application/s in order to:

-Create a New Evolutionary Stone?
-Change all Pokémon who evolve through trading to evolve with this new stone?
-And Possibly change some Hold Items used in trading to induce evolution when used, as opposed to when held and traded?

If anybody can/will help, that would be very much appreciated. Thank you!

You would have to get a program that can edit how to evolve.
Once I made Porygon evolve at Level 35. I can't remember the program though.

Shoot. :\

Oh well, maybe someone else knows of one.

EDIT: I found one, through a few minutes on Google. I actually had to refine the search a lot. I wish I just knew to use Google more often. :\

Anyway, it's called YAPE (Yet Another Pokémon Editor) and all the information can be found here. it's a great program, and can edit just about everything there is to edit in a Pokémon. It includes creating new Pokémon, though it, unfortunately cannot create new evolutionary methods, including stones. It's a great tool, the best editor I've seen so far.

YAPE! Thats the one I messed around with.

It's pretty cool, actually, I've got to admit.

Question, since I'm rather new to the world of POKEMON hacking

Do you guys use programs for everything? No hex editing involved? No ASM? Not even any patches?

There's a program that specializes in just about anything for Pokémon hacking. So yes, I do, but I'm sure there are some people who can hex edit when they want to.