Real legal question: What prevents this "legal hack"?
The simple issue is that the EU market is a rather large market that Apple can't really afford to lose a major portion of. Iphones are a good chunk of their revenue and a lot of that is EU customers. Also, most iphone users get their phones via their mobile subscription and don't buy direct from Apple. Those phones would have to comply with local rules.
When the EU says our way or the highway, the highway could be rather costly. As others are suggesting, all Apple needs to do is certify their phones water proof and/or put a slightly better battery in their phones (> 1000 cycles). That sounds like it should be doable for them.
They'll probably emphasize their awesome new batteries and water proofing of their devices in the usual announcements later this year and that will be it. Expect that to be something you hear a lot about in phone announcements from other manufacturers in the next half year. And maybe some vendors will actually do the other thing, which would be implement actually easy to swap batteries. It might a good way to differentiate in the market. And lots of Android phone makers struggle with that right now.
If Apple wants to keep any of their other services and products, they will also be subject to consumer protection regulation meaning they can’t geoblock consumers and they have to ensure their unsafe products don’t end up with EU citizens.
Software people (generally) have a limited idea of just how complex and rigid customs enforcement can be. Moving physical product between countries is actually a very hard problem.
IMO Nothing legal would need to be done. I think practical reasons like shipping time, shipping cost, and the annoyance of using a phone from one region with telecoms in another region would drastically reduce sales. Also you're not going to get 1st party support and that effects Apple devices more than others.