Do you even use RM? If not, since RM is built as a separate module, you could simply stop using the whole module.
If you do use it, and you need to continue using it in some DM sites and stop using it in others, extending Share while building your own custom evaluator is the way to go.
Check the following link. If you wanted to disable the actions for everyone, you'd simply use the evaluator.doclib.action.disableAction
on beans defining actions you want disabled.
Since you do not want this, you need to build a custom evaluator that would check the site name/description/whatever.
http://docs.alfresco.com/4.0/concepts/doclib-override-extension-examples.html