Hi Christian
I had a test to see if I could achieve this - If you assign the tenant domain manager users to the performance activity manager role at the system level and login as the tenant domain manager you should see
Under activity management - the system level performance activities as well as your tenant performance activities. Note It is possible to see system audiences and your tenant audiences.
However when I go to clone the system performance acclivity this is not an option - cloning tenant based activities is possible.
regards