Mark 1 - According to JAR-FCL 1.330, the privileges of an FI(A) are to conduct flight instruction for a PPL(A), CPL(A), night flying, IR(A), single-engine, multi-pilot type or class rating and FI rating (also, in the UK, the IMC rating). None of these courses, not even the FI(A) course, includes aerobatics in the syllabus. Therefore, your FI(A) rating does not include the privilege of conducting aerobatic instruction in the first place, so how can the CAA seek to prevent you from exercising a privilege of the rating that never existed??? The 'no aerobatics' entry in the licence is quite meaningless - you can teach aerobatics without exercising the privileges of your FI(A) rating and, if you are not using the rating, the restriction to it can not apply.
The fact is that instruction in aerobatics is nothing whatever to do with the FI(A), CRI(A) or any other instructional qualification. Anyone with a pilot's licence can conduct aerobatic instruction, although to receive remuneration it must be a professional licence. Bear in mind, Flyingcircusace, that when you call the CAA to ask these questions, provided that you make it through the automated 'system', you will probably be speaking to someone who knows nothing about the subject and is capable only of parrotting the contents of LASORS.