Is it possible to add a decorator only to members in a certain group?
AFAIK not easily - eg if you decorate a member 3 times (1 for each group) each member is going to have the sum of all 3 decorated files. As for front end / functions you could implement things like group permissions to determine if they can run sections of the code / hide functions from members without that permission.
Hmm, I was really asking because the Member interface already has an export function. May be better to try to add the export function to another dataobject. This is more an idea I'm playing with than a project requirement.