letterbase ... how to user modify

[synergyx]

letter base functions, Purpose to store form letters and dynamically fill in data where needed

Problem; how to allow end user to modify the layout and the content without entering the layout mode. So they can design their own form letters at anytime. And to modify existing form letter content on a per letter bases.?!?!

All I have figured out so far is the need to have these relations within these 3 files

memberID (members file)>LetterLI( letterbase line items file > LetterbaseID ( letterbase file with the form letters)

What I'm stuck on is what kinds of fields & additional relations I need to allow for the above desired effect.TIA