BEags
You are correct on the “Another legal requirement which has probably gone unnoticed is that, from 8th April 2018, if a civil pilot flies aerobatics in an EASA aeroplane (e.g. Grob 120TP), he/she will also need a Part-FCL Aerobatic Rating.”
However, the TPs are military registered as far as I am aware? They were only delivered with G or D registrations.
PS. Looks a bit cramped in the cockpit with the lid down!!