in GB (categories or weighted categories mode) with a standard category (extra credit flag not set) with items
– set the category to be extra credit, then save/close
– re-edit the category
==== result: extra credit setting can be changed (set to not extra credit)
– re-edit the category and set it to be extra credit, then save/close
– select edit on some other category or item in the gradebook, then close with no change (or a change, it doesn't matter)
– select edit on the original category (which was set to extra credit)
==== result: can no longer modify the extra credit setting – grayed out.
There is no way to make a category not be extra credit once something else has been edited. It must be deleted and re-added to get back to not extra credit status. In some cases, you can't delete the category without first deleting previously un-included or extracredit items have different weights/points from the rest of the items, and drop lowest was set.