Sure, you could update a record in a Field Script. An example of that might be selecting something from a Pick List that triggers a script to run and it updates a different field in that same record.
You could also have a Saved Search that fetches the records you want to update and run the script just on those records. You would use search.getRecords() instead of form.getRecords(). Or you can ask the form for a specific with a provided name. E.g. var search = form.getSearchNamed('Action & Adventure'); Then do search.getRecords();.
