Currently "No element in a secondary Option can be referenced by an element outside that Option." is the error that occurs if you try to create a new type of any model element while in a design option. I understand that types can't be exclusive to an option, but please reduce the error to a warning "New types won't be exclusive to the design option" (with a checkbox for don't show again!).
It is very annoying and time consuming to switch back to the main model, create the type needed, go back to the option you were working on, create or modify the piece in question, and then repeat for each new type needed.