If you are a foreign flagged boat you will receive a Transit log (VAT is not applicable) and what the Transit log gives you is 18 months in a given country (may vary country to country). If you go on the hard
like I do after each summer season the clock stops - BUT you have to go to customs
and hand in your Transit log. When your season starts up again you go to customs
again and pay a small fee and get your Transit log and the clock starts again. After your 18 months are up you can sail to another country for a day (supposedly) and return and get a new transit log.
Newly registered boat means you have to get a new Call Sign and MMSI from your flagged country. And then you will need to re-configure this into your VHF. Note some older VHF can only be re-programmed so many times so check to see if you need to get a new VHF - can anyone verify this?
There have been changes taking place in the last year and I believe they are closing loopholes so I would not try and game
the system - if you are from New Zealand - then register it there.
Only downside is you have to leave the EU 90 days in / 90 days out but that is related you to passport not the flag of the boat. As a foreign flagged boat I have not experienced any downsides and can not imagine your situation is any different from mine.