I tried tinkering with it many moons ago, but it seems to be built on a version of the Assassin's Creed engine (forge? I can't remember the name) and there were scarce few tools available. Like all Ubisoft projects this one was also an "offshoot" branch and so had it's own custom modifications to the code making it even more obscure as it was distanced from established AC games which meant even less tools worked with it. In fact the only tool I could find would extract only some files and of those I could only clearly identify image files like parts of the UI or textures for the models... and not even all of those.
I would have loved to try tweaking it, but couldn't find a way to read any of the files much less repack them :/
I've not checked to see if anyone else has made any progress on it or written any new tools to use with it.
GRW also seems VERY tied into being online only play... and I reckon Ubisoft has made more updates to it than any other game so far. I think it is the poster child for their "games as a service" since we are now into a season 2 of additional content (then again I don't play R6 but they seem to get quite a lot of additional DLC and whatnot)
And all this science, I don't understand... It's just my job, five days a week