sounds complicated! I tried soldering/desoldering alps switches once, and a great disaster was the result (I'm holding three carcass boards now in storage, lol). basically my switches refused to work once i had them soldered into the new board. No idea what went wrong, but they were definitely fried, lol.
Oh that's a shame. I had nightmares about this upgrade that that would happen, but I had some success before when I replaced a fake simplified spacebar key that was acting intermitantly on my other kb1903, so I was pretty confident I could do it. A good desoldering tool is a must, and you have to be careful you don't force any solder points. I came close to damaging the printed circuit in a couple narrow parts, but overall the siig minitouch has extremely robust printing, so was fairly easy. The big problem came in the few keys that had bent over pins, they can be a real ***** to desolder.
Also it's a lot harder to get the simplified keys loose because their pins are so flexible compared to the stiff real alps keys, but overall, if you just have a good set of tools you can usually pry the key out.
Also you have to have some minimal precautions against static shock anytime you're working on electronics like that. Try not to touch the board or any metal parts directly.
