Two things

[Baous]

One: Why can't I seem to play any of the hacks in the hacks showcase?

Two: Is there any editing system that allows me to edit the trainer sprites?

Thanks. :)

 

[.Seth]

You might want to check out the ROM Hacking section, as this isn't the right place to ask this. :|
Anyways, here's a link. https://www.pokecommunity.com/forumdisplay.php?f=37

 

[Vrai]

Yeah, as Seth said, this sort of stuff needs to go to ROM Hacking. :x

Anyways, to partially answer your question, the first is because all of the things you're downloading are called "IPS patches". Read up here to see how to work those.

Your best option for the second question is a program called unLZ.gba. Look in HackMew's tools in the Toolbox section. :3

 

[Cherrim]

Yeah, let's keep the ROM Hacking questions over there, shall we? This is not the place.