Another question about shapechange, does true seeing dispel shapechange or does it simply allow you to know that this person is not an actual balor? I want to know if I am facing a person with true seeing on whether I get to retain the benefits of shapechange.
You merely see his true form, but he still benefits from shapechange.
Say a human sorc18 uses shapechange to assume the form of a pit fiend. With true-seeing, you can tell that it is merely a human, not a real pit fiend, but he still gets all the benefits (improved stats, AC etc).