That’s possible, but has some drawbacks. By rotating the entire hanger you do change the angle of the derailleur but also its position, which can cause some real shift quality issues. That would also mean that it won’t behave properly when going back to a bigger cassette too.
The other issue for me is more a principle thing - if I’m designing something from scratch, I think it’s a waste of time and resources to intentionally make something out of spec. A better solution would be a different hanger to fit the same dropout, or to simply not use UDH for road applications right now. I’m taking the last option and starting over - I’ll probably make a dropout to fit Paragon snap ring hangers.