Having opened my FK 2001 just to be nosy, I'd say that someone with even the most basic soldering skills could replace a switch no problem. The solder pads are comparatively huge and spaced out.
Aardwolf, whenever I feel apprehensive about opening something, (which is almost never nowadays, but confidence comes with experience) I always remember an article I read in a magazine when I was replacing the FDD in my Atari ST many years ago.
It said something along the lines of 'The Atari ST is assembled by 14 year old girls in Malaysia. If they can do it, so can you!'
Now, that's not quite true, as I guess those girls probably had some training and familiarity with the design, but the thing to remember is that these things are put together by someone no smarter than you.
A mechanical keyboard is pretty simple as far as these things go, and providing you don't force anything, I highly doubt you'll damage it.
I consider a warranty from a manufacturer in a different country to be pretty much useless simply because of the hassle and shipping times, so I would have punched through that warranty sticker without a second thought!