If Koi spends 183 days outside of Minnesota, he's not a Minnesota resident for tax purposes. If he's at Texas Tech starting spring semester and is there throughout 2026, he can be a Texas resident for tax purposes. I don't know if he has to do anything other than that to establish residency. The whole NIL thing is pretty new, but I'm sure the agents and accountants are laying out the options for the players and providing them with advice.
But I do laugh about all the talk about players making decisions about where to play based on state tax policy. A tax professional can correct me if I'm wrong (and NIL may be treated differently), but professional athletes and entertainers have to pay taxes in the state in which their services are applied. In other words, when the Texas Rangers and Houston Astros play the Twins in Minnesota, the portion of their income attributed to those games is subject to Minnesota taxes. Same when a rock band plays a show here (at least that's the way it used to be). I remember when Al Franken was running for the US Senate and it was found out that a relative who did his taxes was unaware of that, Franken owed taxes in multiple states (but was due a refund in Minnesota because his income attributable to what he earned in Minnesota was overstated). At least that's what I recall and admittedly I could be wrong. Tax pros, help me out!
But what is even more hilarious is that if tax policy had much of anything to do with it, the Florida Marlins, the Houston Astros, and the Texas Rangers would have the best teams in baseball because those states don't have a state income tax and the Dodgers, Giants, and Padres would all suck. Tax policy may play some role for some guys at the margins, but when guys are making scads of money it probably doesn't make a lot of difference.