I agree that the UK orphan designation is automatic. All an orphan designation says is that the indication is small. It says nothing about the drug.
Additional indications do not just get added. The entire point is to assist developers of drugs for small populations.
Now, for rGBM, that is just a subset of nGBM (despite what ATL and diver think). Nobody has rGBM who did not have nGBM.So yes, that would also get orphan designation.