First time I replaced the cambelt (AMF engine) I later decided to do the 'torsion' timing check with VCDS. As you found, the plastic cover seems loose but won't actually come off. Well I persevered and applied some controlled brute force and it did come off. Thought I'd got away with it but found a 40mm split on the side flange. The cover is not sealed and I thought about trimming the plastic so it could be removed easily.
I never did. the split has not grown and it gives enough 'spring' in the side flange to slip over the pulley
Cheers Spike