GKR,
If I understand you correctly, you want to override the behavior of a
Field.choices property, so that admins can add values on the fly. I
don't think that is possible with Django.
Maybe the best solution is to create a new table with one column - one
that contains only the choices admins want for particular fields in a
parent model. And then use the magic of InlineModelAdmin objects to
embed that table in the parent tables's admin page.
https://docs.djangoproject.com/en/dev/ref/contrib/admin/#inlinemodeladmin-objects
Is this of assistance?
Best regards,
Peter