From what I recall the 'SHW class' was already in the game. In the bot file, there is some ID line where something like 0 = LW, 1 = MW, 2 = HW. SHW had some awkward number like 110158112 that was basically like a test weightclass or something just left in the game but never used. All we did was make an icon for it. What I mean is we didn't add the SHW weightclass to the game, it was already there.
However, I don't think it is possible to add other weightclasses into the game. I'm pretty sure we would need to be able to edit the .exe to add custom ones, and we are not able to do that unfortunately.