[Koha] "Unlocking" the 100$a cataloging-field

Me again, hello, i try to add a own framework for our needs here, since almost nobody knows about the MARC Things and so on and i want to make it easier for them. But the 100$a authors field is locked, i can't fill something in. So i went to Administration, System Parameters, and changed BiblioAddsAuthorities to "should". But it is still locked. Is there a second location, where i need to change something? Thank you again. grex