You can rotate it back by 3 degrees and still be within UDH spec.
The problem with rotating it back more is that if you ever want to use the hanger, the derailleur attachment tang will be indexed incorrectly.
But as you say, no bigge if all you ever want to use is a T-type mech. It also wouldn’t be extremely difficult to just do a quick mode to the hanger if you find yourself needing to use one.