I've tried a lot of things: Changing file names, editing file paths, editing Oblivion_default.ini, editing the goggame-1458058109.info but nothing I do works. It's like Galaxy is actively circumventing my changes and it's getting annoying.

Anyone able to assist? :)

Would you not launch obse via mod manager? Anyways, obse is just an exe you drop in your oblivion folder and then run rather than oblivion.exe. So theoretically just swap out oblivion.exe with obse.exe and you should be fine. Although I don't know galaxy as I wouldn't install the garbage on my system.