Git: Ignore tracked files

Sure.

git update-index --assume-unchanged [<file> ...]

To undo and start tracking again:

git update-index --no-assume-unchanged [<file> ...]

Another approach (from a now deleted answer by Seth Robertson, but I found it helpful so resurrecting it) is to maintain a "tracked" template file, then have local untracked version of it, ex: "config.sample.ini" or "config.ini.template" see https://gist.github.com/canton7/1423106 for a full example.

Then there won't be any concerns if the file is changed within git, etc. and you can use .gitignore (finally) on the local untracked files.

An another solution using git attributes and %f in filter command:

git config filter.orig.clean "cat %f.orig"
cp filename filename.orig
echo "filename filter=orig" >> .git/info/attributes
echo "filename.orig" >> .git/info/exclude