Using the above script, yes, a set field step could be used to set a field to a value. This can be a straightforward thing that simply replaces the value in the field with a new value or, when working lists of values produced by clicking check boxes, it can be used to append or remove just one value while leaving other check box values unchanged.
But you can also use Replace field contents as a single step in place of your entire loop also.
How would a single step account for the looping of all records that are selected though?
Ignore my last loop question - I just realized I can use the existing scripts from the existing buttons lol Thanks for you help though!
"How would a single step account for the looping of all records that are selected though?"
Replace Field Contents can update every record in a found set so it's a matter of pulling up a found set of your selected records.