The current view in the UK CAA is that you follow the rules of the license you hold, so if you hold a JAR license (even one deemed to be an EASA license) then the old rules apply, ie. only differences training required to move between A109 variants. As soon as you change to an EASA license you need to be very careful to ensure you get the right types put on it. If you've been flying both Allison and P&W powered machines, you need to get A109 (Allisons) and AW109 (P&W) types on the new license. In other words, do your differences before you change your license !
HTH