I don't think you have to get your meter resealed and re-verified unless you took the security stickers off? The time on the meter on my old Octavia used to wander a bit. It was only a ten minute job and a €15 for the guy in the garage to set the correct time. On top of that, most meters allow you to change the time by a couple of minutes every week or two, depending on the model & if you remember.
Re the licence renewal retest (or suitability retest), I think you just ring up and rebook. Why are you going down to Athlone? If you rang tomorrow, you'd probably get a retest in Ballymun next Mon or Tues? The price is the same, as far as I can remember, but it's an expense against your tax bill so not the absolute end of the world.