I would not put this data in the same field. I'd put the date in a date field and the user name or other text in a different field or fields. That keeps your date in a field where you can treat it as a date instead of as text.
There are some key combinations you can use to in conjunction with the OnObjectKeystroke trigger See also the Get ( TriggerKeystroke ) and the Get ( TriggerModifierKeys) functions in FileMaker help. But many ctr-key combinations are reserved for tripping OS functions and cannot be set up with this trigger.
You may also want to set up a field to auto-enter the user name or account name each time that the record is modified as a way to capture that information.
I'm doing this now! New table new portals for adding notes with date ...
Big job but worth it!