resync ports?

Hello,

I had to make a change to a makefile to make that port compile. Now I am 
wondering how to get the original makefile back, in a way that it is 
controlled by git again?

Somehow I expected git pull to work like rsync, but it is obviously not.

The question that emerges, is there a more resourcefriendly way to get 
my portstree back in sync with git without a new full checkout?

Thanks

Ede