Any time you’re given an illegal assignment it pays similarly to the language described in the PWA for inverse assignments. Look at 23.U.3. Hence why a reserve only gets “A day” pay (first duty period language).

look also at 23.U.6. for some pay examples on inverse assignments (removal of a rotation addition of another). It’s not written in the PWA but any time it’s an illegal assignment it then also leads to the company being required to identify and pay an affected pilot.