[Koha] adding MARC tags (not in framework) while cataloguing

Hi, I occasionally need to add unfrequently used MARC tags to new records, even though they are not present (=active for staff) in the default MARC framework. I realize that it is possible to activate those tags by (temporarily) modifying the default MARC framework, or that one can save the record in MARC format, edit it via MarcEdit, and then re-import the record, including any additional tag. Isn't it possible to activate MARC tags at cataloguing time? Many thanks and best regards, Giuseppe.