That helps thanks. So note for now I just copy/update my entire gitconfig and replace the one off changes every so often.

Its not ideal but each difference is really an entire file. I worded my question poorly in that regard but i'll have a look at dotdee.

I'm somewhat tempted to just use m4 for generating the dot files for things that may change and doing a conf.d type setup that just lets me copy a fragment file into place then instantiate the file.