Oh sorry
I mixed something up. Sorry for that.
But I have a second idea: You can create a new Cube with the new high level dimension. Create an active form and join the values from your original cube with an additional view. Maybe you can try this.
create an additional dimension and insert all elements the user should be able to see.
After this open your active form and change the dimension in the rtprow-function to the new one. This should work:)