Mike Jackson had an article in SignCraft a few years back with that exact scenario I mentioned. He built a
sign for a restaurant and figured the square footage down to the inch. Later the customer wanted to add a beam to the bottom that read "RESTAURANT". Because he had figured so accurately he was able to add to the
sign since he has some extra footage to play with.
There have been more recent articles in SignCraft that cover this very situation, can't hurt to ask when pulling the permit anyway.
Maybe someone can remember the article that Mike Jackson wrote, huge
sign with an elk and crossed rifles. I guess Jackson Hole Wyoming is different (lenient) than other towns.
Anyway Flexi will figure it for you, which was the point of the question. How you use the info is up to you.