I was hoping for a way to eg. set diff settings based on installed programs, but seems to have reached a compromise in that including a file which doesn't exist

I was hoping for a way to eg. set diff settings based on installed programs, but seems to have reached a compromise in that including a file which doesn't exist doesn't cause any visible errors, so I can just use a systemd-esque system where I include all the files and create them (as symlinks) when appropriate.