Long story short: completely stripper the hex slot on the back of the freehub body while trying to remove it. It’s incredibly tight. Can I just take a pipe wrench to it from the front or do the teeth seen here on the new part lock with the wheel hub making it impossible to turn?
If that freehub is constructed like the ones I’ve taken apart before, you’re out of luck. Like you suspected, the teeth lock the rotation of the freehub to the hub, unless the screw in the back is taken out first.
You can try hammering in a (slightly larger) torx key or using an easy-out (probably won’t work if it’s very tight).
As a last resort, you could try to drill out the screw (only so far that the freehub comes off, you don’t want to drill into the hub). Then you should hopefully be left with enough left of screw to grab with a pipe wrench.
Yeah I think I’m just going to disassemble the new one and move all the parts onto the old freehub body. There’s no way I’m getting this one off without messing up the wheel hub. If correct size allen key and a 2 meter long cheater bar didn’t get it to budge I don’t think the torx method or a screw extractor is going to work either.