I think it should be possible to do it for anything, if you have have a monotonically increasing file version number that has no bearing on the release of astropy.  You run into issues if you add something during development and later backtrack on that idea.  You can also have problems with merging (i.e. two different branches each wanting to update the file format), but I think that will be rare and git should hopefully complain about those kinds of merges.