Cacher is the code snippet organizer for pro developers

You could update your index:

cd /root/folder/of/your/repo
git update-index --assume-unchanged nbproject/project.properties

and make sure it never shows as "updated" in your current repo.

That means it won't ever been pushed, but it is still present in the index.
(and it can be modified at will in your local working tree).

to revert that state (from git-ready):

git update-index --no-assume-unchanged 

to see all assume unchanged files (from Gabe Kopley's comment)

git ls-files -v | grep '^h '