extesy you are a hero for making these instructions and the new dat file. This is exactly what I was looking for. It's too bad I had to spend like 20 minutes searching to find this thread. If the dev/gog aren't gonna streamline this, they might as well point everyone to this post.
Though, it is still sad I have to use the bandwidth to redownload 40+ GB for each expansion, only to delete them to free disk space. Considering the DRM-free nature of gog especially, they should just make those couple GB files in the bin_addons folders available for purchasers.
Also as an alternative to what powergod said (since I am no longer concerned about updates past this point), I just turned off auto updates and then pointed soul harvest to the Reforced exe. Then I could keep using gog as a launcher. Basically, in my attached image, I switched the default exe. Any of the 3 games can be launched in galaxy to then play any of the content. But which one you choose to launch will determine where gog tracks your time, etc.
They are actually working for an update, but are having issues. The last version should already work if you copy the expansions in the reforced folder, without the need of the file pointed here.
More updates will follow.