I wrote a very simple command line utility that I associate with .3dm files in Windows. It queries the header information and runs the version of Rhino that matches the file. It was someone else’s idea, but I was surprised how useful I found it for opening files downloaded from discourse. Opening a Rhino 5 and Rhino 6 - #11 by jeremy5
If I had similar header info in .gh files I could extend it to do the same thing (and if the header info was in the same format as in the .3dm files I could just add the associations to an .ini file without needing to change the code).
Jeremy