Well I don't know how it would work in terms of programming. Maybe something along the lines of a preference panel where the user can assign another field for duplication of any codes that are entered into the caption box. Maybe even specify what type of code as I'm sure people use code replacement for text strings other than people's names.
So the preference could look like this:
[Check-box] Copy code replacements to 'Keyword' field when entered
[Check-box] Ignore code replacements beginning with [User defined key]
The destination field would be user defined also, so a user can choose another field, possibly a custom field set-up for that purpose.
As PM is already on the look out for \code\ when the final '\' is entered it will not only past that particular code to the caption but also to the other user defined field.
But for me, and I'm sure a lot of other agencies who world with multiple photographers, would be an update button.
What I would like is to keep my code replacement file on my server, possibly as a web page. I would then give the URL of the file to my photographers who will enter it into the preference for code replacement just like a file is now. When PM starts-up a box will appear asking 'do you want to update your code replacement file?' If the user clicks yes then PM will go to the URL and retrieve the file, or list of codes, overwriting the previous settings.
This will allow all the photographers in a group to work with only one master code replacement file, and when that is updated, everyone gets the update, instead of sending out new files and photographers having to manual remove the file and enter a new one.
This could also work for IPTC Stationary templates. Online would be a caption file with, maybe with the photographers initials and then the date, again from a pre-defended URL. When the snapper goes to ingest his images he clicks on a button that says 'Get today's caption' and PM will go to the URL and retrieve a file called AB070104.ipc (or AB{iptcdate})which is the photographer's caption for that day's event. Obviously the caption would be written before hand, but an editor can write out captions for all his photographers for forthcoming events and place them online. This would reduce the amount of captions written incorrectly with erroneous keywords and keep the style the agency wants.