From the top of my head I think you could add an action for the post-backup-data event.
Put your script in /etc/e-smith/events/actions/ with executable permission. Give it a descriptive name.
Then link the action to the post-backup-data event:
cd /etc/e-smith/events/post-backup-data/
ln -s ../actions/yourscriptname S90yourscriptname
Replacing yourscriptname as appropriate.
Haven’t tested this but think it will work (unless you find a permission issue).