When you put a soldering iron on the board you can damage 1 of the layers and crash the whole board.(because you got the wrong part too hot) If you don't have the right tools to remove the old solder you run a real chance of creating a short by getting solder somwhere it shouldn't be. If you just yank it off, the board itself will break most of the time before the block comes loose. Also a circuit is ending at that block depending on how the manufacturer laid out the board it may or may not run after you pull it.

I learned most of this by either doing it or fixing the mess after someone else tried and had me put the pieces back together.

I didn't say it wouldn't work I just said I would recomend against it because your running a 50 50 proposition at best. Believe it or not if you scratch your board (not even that deep) in the wrong spot it can die. The manufactures claim a simple static shock can kill the board, I haven't seen it happen but I have talked to people who have.

Don't get me wrong I've broken out the hack saw and dremmel plenty of times. But I have cooked one or two to many boards trying to get that extra eigth inch of clearance. When I do this it is in my repair room and usually on an old computer which I have about twenty of laying about right now, and the stack is growing. If I find something that works with consistancy I'll do it on newer stuff.