By 30 July 2017 UCITS will need to comply with the terms of the ESMA Share Class Opinion. 

Helpfully, the Central Bank have indicated in their Q&A that prospectus updates can be carried out "at the time of the next update of your prospectus".

But away from the prospectus disclosure/transparency aspects, UCITS should also be reviewing their operational processes to ensure their share class currency hedging techniques comply with the provisions in the Opinion (and the Central Bank's corresponding Guidance, as updated on 28 June 2017).