I've found a couple of different discussions that kind of relate to my problem, but with different workarounds and solutions, so I thought it best to pose a new question and get a general concensus on how to tackle it. I suspect this is something that a lot of users would need to be able to do.
We have an incident process with various "Add Note" action instances (not automatic), which are then each followed by a corresponding "Add Reminder" automatic instance. The various "notify" values for the reminder form are carried through from the note form (ie. we have "Notify Assignee", "Notify End User", etc. check-boxes on the "analyst" note form, and the "Add Reminder" automatic instance has runtime values on the corresponding check-boxes like "Incident/Notes/Notify Assignee", for example. However, we don't currently have any of the "notify" check-boxes on the "end user" note form (used for Web Access), and don't particularly want to, however we do want the "Notify Assignee" to default to True when an end user adds a note.
I know that I can set the default value to True for "Notify Assignee" on the "Note" business object, but if I do that then the same check-box is also ticked by default when an analyst goes to add a note (and assuming that in most cases it will be the analyst who's assigned the job who'll be adding a note, it means they would have to specifically untick that check-box everytime they add a note).
What I was thinking (or hoping) that I'd be able to do is set the default value for various controls on an individual form - eg. put the "Notify Assignee" check-box on our end user "Add Note" form, make the check-box read-only, but set its default value to True - without the specific need to set that default value on the underlying business object itself.