OB32 - Document Change Rules for Recurring Entry Document

I am trying to enable a field to be changeable during transaction FBD2 (Change a Recurring Entry). This field is "transaction type", COBL-RMVCT. It appears during FBD2 under ">More", Coding Block. I have added this field to OB32 but the field is still greyed out in transaction FBD2. Does anyone know how to change a field under a Coding Block or under "Change a Recurring Entry"? I want to change this field before running 51 recurring entries without having to delete all of them and recreate them.