G-reg ownership requirements

I would bet that the stuff under the control of the UK CAA will remain “indefinitely”.

And it is them who decide the owner qualifications for a G-reg.

The country where it is parked can implement whatever long term parking limits it wants on foreign reg (non EU) planes. EASA has no say in this – example.

Can the (non-UK based) EASA-certified maintenance shop continue to maintain a G-reg acft as if nothing happened or not

IMHO yes, because this is up to the state of registry ie the UK, and the UK has no interest in screwing its own people, or people flying its own reg planes. Historically its policy on this has been constant for a long time.

The supporting argument for the contrary view would be in the form of retribution (revenge) for the EU having screwed it in other areas ie using foreign based G-regs in the same way as Spanish based Brits The reality is that the UK doesn’t want those Brits back because the main reason they would come back would be for the national health service benefits and Spain doesn’t want to lose their spending either. But they will be a theoretical pawn in the negotiations on immigration policy. But nobody in power in the EU gives a damn about these G-regs, so it is a really weak pawn.

So I think EASA Part M will remain acceptable to the UK CAA.

For me that’s a big factor on changing registration or not.

You can probably change it at any point without too much trouble. Well, so long as the plane doesn’t have mods which have dodgy paperwork which the last CAA’s inspector didn’t spot And this has happened… but you won’t be reading about it. Transferring regs within EASA is not always a straight paper job.