Fork locks have been done, though, which would prevent steering.

Looking at Michigan's laws... MCL 257.662(1) doesn't actually say that additional lights aren't allowed, just what's required. It is confusing about the whole rear light thing, though. However, MCL 257.657 may allow a bicycle rider to follow car or motorcycle lighting standards (because they are applicable to a bicycle).

Here in Ohio, things are much, much clearer. ORC 4511.56(B) is explicit that red can't be on the front, and white can't be on the rear, but anything else is fair game. (Pretty sure blue would be a bad idea, though.) Then again, there is the conflict that ORC 4513.17(D) presents, where vehicles (not just motor vehicles) cannot display a flashing red light unless they're public safety vehicles or school buses. (Which actually conflicts with the fact that red turn signals are legal, too.)

And, signalling with the right arm for a right turn is legal on a bicycle in Ohio.