If you are even quasi-interested in working on your own 1911's, I highly recommend buying the Kuhnhausen shop manual (vol 1) first thing. It's a very thorough and helpful reference, mostly for the "this is how this part is supposed to act" and the "when removing metal from this part, DO NOT change this angle" advice.
You will end up buying it sooner or later... how many mistakes are you going to make before you buy it, though?
Having gotten that off my chest, dropping in a hammer isn't difficult. Depending on the maker, you may have to do some to no fitting. As long as it works like it's supposed to (safeties work as designed, hammer doesn't follow slide, etc.) you won't have a problem. But be advised that many elongated hammers won't work with the factory grip safety. Most aftermarket grip safeties are relieved to accomodate the longer hammer.
So you can see that there can be something of a domino effect when working on the 1911.
Installing a new trigger is easier. Might as well buy a new sear spring to help lighten the pull somewhat as well.