Rule 1 Don't change anything until you need to.
Rule 2 Be aware that there is a simple conversion process to a JAA PPL which will "automatically" become an EASA PPL.
Rule 3 Don't leave any conversion too late as there is a load of tripe being talked about conversion criteria. An ICAO PPL is an ICAO PPL at the end of the day and you don't want to be involved in meeting additional requirements.
Most JAA PPL candidates can't demonstrate radio nav adequately on the Skill Test, so requiring experienced National licence holders to demonstrate this as an extra is nonsense. If we go back far enough there wasn't a Nav Test at all and no IF was taught! Will they have to do additional training?
The CAA have recently told some Examiners renewing after a lay off, that they must get a JAA licence if they want to be re-authorised, even though there are currently no requirements to do this!