Much like with the PDF copy of the finding aid, the processor will highlight any changes made to the MARC record if the collection already has a MARC record in the University of Michigan Library Search (public link).
If the processor wishes to add new agents or subject headings to MARC records, they should add the agent or subject heading to MARC record template, and add a comment that 1.) provides a link to the term from the appropriate resource and 2.) note that it needs to be created AND added to the finding aid.