Thank you all for your thoughts. But with regard to Matt H's question:
"what happens if I distribute an actor built in mode C and a less experienced user accidentally switches it to a different mode while editing it or checking out its internals. I foresee an increase in emails about my actors not behaving as expected."
This is not a problem unless the user chooses "Save and Update All," and if they're doing that with someone else's User Actor (especially one as generlized as yours) then they will simply need to accept what happens.
On the other hand, one could "bulletproof" the User Actor inputs and outputs by setting specific Absolute Min/Max (i.e., to something like -100 and +100) so that no other customizations on the outputs would be needed.