[Answer]-Manipulate m2m records in django admin's save_model method

You can either connect to the m2m_changed signal https://docs.djangoproject.com/en/dev/ref/signals/#m2m-changed, or use Django 1.4’s new “save_related” – https://docs.djangoproject.com/en/dev/ref/contrib/admin/#django.contrib.admin.ModelAdmin.save_related which closed ticket 16115 https://code.djangoproject.com/ticket/16115

See also https://stackoverflow.com/a/8462541/640759