I still don't see much of a point to this as there's already a separate Galaxy installer and no-one is going to need to install Galaxy every time they download a new game. The inconvenience it causes is not worth it and makes things unnecessarily confusing, while also giving the impression that GOG is trying to get rid of the regular installer. Calling it the classical installer also makes it look even more suspicious as classical implies unchanging, rather than something that is being kept up to date.
If you want to avoid over complicating matters while further pushing for Galaxy, wait until until you've made the small Galaxy file and then put it in the regular download menu in addition to the normal installer and the Try Galaxy button.
JMich: Let me (once more) suggest the following as a method for the installers.
Have two exe files for the setup, one with and one without galaxy. Both these exe files use the same .bin file(s) for the game files. If you need to do changes to the installers, only the .exe files change. If you need to do changes to the game files, only the .bin files change (though it would probably be a good idea to also change the .exe files to look for the newer .bin files).
It would need to recreate the installer creation process, but it should result in a better end result, and possibly better workflow.
This could also work and then you wouldn't even need a separate tab for the Galaxy and regular installers while reducing the workload and number of potential things that can go wrong.