EU law does not recognise, per se, the concept of 'grandfather rights'. Previous experience may, however, be credited towards the issue of Part-FCL licences and ratings in accordance with a 'Credit Report', prepared by the competent authority in consultation with EASA. One may suppose that a credit report will be prepared in respect of previous aerobatic experience but it is doubtful that this is currently high on the UK CAA's list of priorities. As BEagle correctly points out, the aerobatic rating is not currently intended to become a legal requirement in the UK until 2015, although that's not so long given the CAA's usual work rate.