I kind of ruined the tuning pegs on my previous guitar by not taking them out properly. I didn't realise that you could push the string into the hole a little to loosen them up before pulling the peg out, and often resorted to pliers which totally warped the heads. I've avoided restringing my current guitar, bought by my wife as a wedding present, because I was afraid of causing similar damage (even if the pegs are easily and cheaply replaced).
It's been losing tune recently though, so I knew I'd have to replace the strings at some point; I've had a fresh set in a drawer since Christmas, so I finally took the plunge this afternoon - and apart from one, the pegs all came out pretty easily. I'd also never thought of putting my hand into the body to push them out from the inside on the old guitar, so that also helped avoid damage.
The only downside is that I'm terrible at tuning guitars. I can't do it by ear at all, and my tuner is oddly sensitive on some strings and seems to be unable to "hear" others. I eventually managed to get it sounding more or less okay, at which point I went right back to boring everyone to death by practicing Spirit First for the rest of the evening.