Your FAA PPL is still valid as long as your Irish PPL remains valid and current.
Remember you will need a Bi-annual flight review and relevant endorsment to actually make your FAA PPL Valid in accordance with FAR 61.56.
The only way to change it to be based on your UK CPL is to re-apply completely...and that costs circa £38 with the UK CAA.
Where I completed my training, the DPEs would accept the letter of verification if completing a Commerical or Instrument upgrade, (Be aware a letter of verification is REQUIRED if completing more FAA licences/ratings and it MUST be valid, to prove your licence hasn't been suspended etc..) even if you had your CPL issued since. It's only a change of the PP to CP before the licence number.
Last edited by BigGrecian; 29th September 2006 at 14:51.
Reason: Talk about completing further FAA ratings.