Want to change Incident-Add'l Field format

We would like to change an existing required field on Incident Templates from Multi-Line Free Text Format to Multi-Line Pick List. Is this possible without creating a new field and editing all the templates?

Example. Currently "Department" is a Required Field for a "User Security, Menu, Directory Change" Request. The field is Multi-Line Free Form Text.

We would like to make this field a Multi-Line Pick List. Thereby bringing consistency in input by users. Option to select 1 of 14 designated departments.

This eliminates misspelling, abbreviations, inconsistencies in classifications.

I was able to successfully change the Service Request Additional Field for Department but cannot change for Incident Additional Fields.

Is there a way to change the Incident Additional Field as needed?

Thank you,

Cheryl