I'm on MCGalaxy 1.9.5.3, I did /update latest, and I want to add more custom blocks (more than 255) without having to rebuild the server (create everything again). I tried switching the MCGalaxy_.dll file with the MCGalaxy_infid.dll and renamed the latter to MCGalaxy_.dll and moved the original away, and it doesn't start. System specs are attached.

Where did you get the MCGalaxy_infid.dll? If it came from the "Uploads" folder on github, that is no longer updated.

Try using the MCGalaxy_.dll from here: https://123dmwm.com/MCGalaxy/

Thanks, now it's working!