That's interesting. When I changed jobs and moved from NY to Indiana, so my wife could pursue a graduate degree, I had every intention of maintaining my ID and permanent residence in NY, (since I could always still receive mail there via my parents, who allowed me to maintain my permanent residence there whenever I rented or was resident in student housing.)
It quickly came to my attention by communicating with car insurance that I could not do this legally (they sought me out, I have no idea what caused this, perhaps a National Change of Address record triggered?) my car insurance would be terminated because my car was no longer "garaged" in NY, and a lack of insurance on my vehicle registered in NY would trigger a suspension of my license, (and eventually a bench warrant could be issued potentially leading to my arrest, if I did not take action before 30-60 day window passed.)
I wonder if you got lucky, or if this scenario doesn't play out the same way in EU? FWIW, it turned out that everything about being an Indiana state resident is cheaper than living in New York, and it really was to my benefit to get my home permanent residence changed to the new state.
(It was very surprising that I had to do this, though, as a student you are allowed to maintain your primary residence in a different state, I guess this justification works for undergraduate but not for a spouse's PhD study...)