svn up file
Git doesn't work on individual files. I'm not aware of the
remote_cache setting so I can't comment on that. However, in git, you have to
clone the entire repository, make a change to a file(s), commit it (this is a local operation) and then push the changes back.
In your setup, you should be able to simply
pull the changes from the master repository (call it M) to your capistrano deployed repo(call it B). I don't see why you're having the problem. If B is substantially different and you don't want to mess it up, you can add M as a
remote to B and then
cherry-pick the specific commits you're interested in (i.e. the update to the file you're talking about) into B. Would that work for you?