So how hard is it to change a stock, and what kind of tools would I need to do it?

Keep in mind that besides cleaning, the most complicated assembly of my AR that I ever did  was attaching the upper half to the lower half.

It takes a screwdriver and its easy. You might want a stock wrench if you're putting a collapsing stock back on.

I switched from my A2 to one of TheTic00's 6 positions in about 30 minutes.  I used a large flat head screw driver for the big screw in the back (top one) of the A2 stock, very small flat head screw driver (to hold the buffer retaining pin down) and the stock wrench I ordered from him with the stock.  It's VERY easy, use this link to make sure you do it right and READ AHEAD or you will lose parts.

Ditto absit;  what I suggest is once you get the buffer tube broken free (and before you unthread it more than one revolution), put a rag over the back end of the lower receiver.  That way, when you make that next turn on the tube and the buffer retaining pin SPROINGS out, it'll be caught in the rag (and not shot over into the corner of your cobweb-filled garage).

That happened to me twice.  In the same day.  About 15 minutes apart.