Glock says that using any aftermarket part which affects function will void your warranty. They also say that disassembly of the gun past field strip by anyone other than a Certified Glock Armorer will void the Warranty, as will using any ammo that is not factory new jacketed ammo which meets SAAMI specs.
The fact is that they'll only refuse Warranty Service if there's a major component that needs to be replaced and it's obvious that one of those things caused the problem. Many people have sent their guns back to Glock with aftermarket parts installed and Glock replaced those parts with factory parts, then put the aftermarket parts in a little bag that was shipped back with the gun. Sometimes they'll actually charge for having to replace aftermarket parts with factory parts.
If you install a new slide stop, make sure that the locking block pin is installed in the frame before you put the slide stop in the frame. Here are some detail strip resources that may help you:
On the following page are some Glock Armorer's Manuals, just scroll down to the "G" section. I learned from the Update Manual and 2009 Manual. The 2009 Manual has a few pages missing, but that info can be found in the Update Manual as well.