1-most of my desoldering attempts look a little singed, did I break the pcb with every attempt?
2-Do I have to desolder every switch and those locking plate brackets to remove switches, or can I just desloder 1 switch and pull it out?
3-Related to that, is there a way to do that safely without damaging the pcb?
4-The big metal clips that hold the pcb to the plate are extremely hard to desolder at 750 degrees for some reasons, I managed to get one done, but failed at the other. Any tips?
1. That's the flux, most likely added when you added some solder (good on you, that's exactly how to do it right) It's just fine.
2. as TJ said, you can pull them out one-by one if you want.
3. What I do is desolder the one switch in question, then get a nylon stick to press in the tabs on the top and bottom, and pull it out from there. I press up on one tab, hold it in place with a fingernail and unclip the other tab, then it pops out.
4. Yes they will be extremely hard to desolder since they are big metal clips they act as a heatsink and have a huge thermal mass. I recommned leaving it as-is if at all possible to avoid PCB damage.
note: some of the switch pins are bent over, You get that sometimes. It's possible to lift it up off the PCB with the soldering iron tip or with a tweezers.
on some of the pads that only have some of the solder removed, put a lot of solder on it and heat it thoroughly, mixing the old and the new: should be very easy to desolder after that.
Poker has plated through holes and is pretty easy to solder and desolder, DAS depends on the generation.
hope this helps.
edit: btw what keypad is that, It's really clean.