Physics is not like art or graphics or sound; it is a core part of your game. It is part of what makes people want to play your game.
If Box2D has "features that I really like" and Chipmunk does not have those features, then you cannot develop your game under Chipmunk. Unless those features in question are fluff or otherwise superfluous. If they are important to gameplay (constraints, rigid body dynamics, etc), then you will need to have them in your prototype before you can consider your prototype complete.
The problem is that the Python port of Box2D is pretty tedious to install and I'm lazy
If you truly are, as you say, "lazy", then perhaps game development is not the hobby for you. Game development requires work and effort. If taking a couple of hours to compile and install a Python module for a library is too much for you, then what are you going to do when you hit a real problem? When you can't figure out how to make the various objects interact correctly? When your AI seems to be doing the wrong thing and you can't figure out why?
That's no excuse for a difficult install process. But if you need this library, then you should be willing to expend some effort to getting access to it.