The worst you can do is lift a pad and/or burn up a trace. Keyboards are pretty forgiving. If this happens, you can usually either (carefully) scrape the solder mask off of the trace and run a jumper wire from the switch leg to the trace, or play around with some scrap wire bridging the undamaged pad to other nearby pads until it registers the correct key press and run a jumper wire from the leg with the damaged/removed pad to that other switch leg/pad.
You want to heat the pad only as much as necessary to melt the solder, and only for long enough to remove it. If you can help it, you don't want to put any stress on the pad (including trying to firmly move the switch leg when there's unmelted solder still bridging it to the pad. It seems to me that lifting a pad is most likely when the pad is hot but the solder isn't quite melted.
As far as tools go, I have only used Chinesium manual pumps. I think one was Radioshack branded. They were a nightmare. I spent almost as much time unclogging them as I did using them once I got the timing right to actually get all of the solder from a single pad in one go. I have heard good things about the higher-end ones by comparison, but have never used one. I have not used the more reasonably-priced combination iron/pumps posted here either. I figured I would be doing a lot of dumb swaps on ancient boards for kicks and giggles, so I jumped straight to
one of these bad boys. With this (which have adjustable heat settings), it generally takes me just a few minutes to desolder a whole board if the old solder is decent leaded solder. I like to give it a moment to melt all of the solder on the pad and simultaneously turn on the pump and wiggle the nozzle in a circle. Unless the pump is clogged (yeah, that happens even with these) that usually cleans the whole pad and switch leg of solder in a second or two. If the solder doesn't seem to want to melt, add some fresh leaded solder like mentioned above and/or flux and try again. Some solder OEMs use is pretty terrible.
Once all of the switches are free, the plate should come right off with no force. If you get any resistance at all, double check all of the switch legs to make sure there's no residual solder holding them in place. If your pump isn't that great and/or the original solder isn't that great, you may need to add some quality solder back to the pad/leg and remove it again in order to free it.
You can pull the switches out of the plate with a switch puller like are included in some cap pullers. I usually just pop them out with my thumb once the whole plate is off. When you put all of the switches back into the plate, make sure every single one is oriented exactly as they would sit on the board. Sometimes switches are meant to be installed sideways and it is
REALLY easy to bend pins if you try to put the plate back on with any in the wrong orientation. Also make sure that you're not inadvertently using pads not intended for your layout (I can't tell from the product page whether or not the PCB in that kit has solder pads for Windows keys regardless of chosen layout (I would be surprised if it did not).
Once
everything looks correct to your eye, you can carefully line the plate up with the PCB and lower all of the switch legs into their corresponding holes. If you meet any resistance, check to make sure that none of the switch legs are bent and bend them back to where they should be and try again. The last thing you want is to rush this and realize halfway through soldering the new switches in that you bent the legs on a few switches. I usually eyeball the legs of every single switch before I even start soldering them into place ... because I have bent some pins in the past without noticing.
When you're ready to start soldering new switches in, you may want to check and see that the big center nub on the switch is relatively center and recessed reasonably well into the hole for it in the plate. You may notice that some of them are not centered and might need to wiggle everything to line it all up reasonably well. If any of the switches seem more shallow than others, I usually just press the PCB into the plate in that area and once they seem relatively flush I'll solder a few switches in that area into place (You don't want to release downward pressure on the PCB until the solder of at least a switch or two is dry again), and repeat for any other areas that look shallow until every switch (soldered or not) looks relatively flush. You obviously don't want to adjust this later when you've already got switches soldered into place near a switch that's sitting somewhat shallowly in the PCB, because then you would be pressing directly against the pads. Only then do I solder all of the rest of the switches into place.
I don't do lube, but I do one heck of a lot of switch swaps, so the above should be helpful. All previous comments are sound advice.
