I ran into this same issue when I was looking at the Sig P250 as well. I called MSP and they advised that I had to register the gun in the configuration it was purchased in with the details specific to that configuration. I asked about issues with changing out the configuration after registration and they advised it would not be an issue since it is manufactured and sold with that capability from Sig. They did say I might have to explain it to an officer if the registration was run for some reason but that there is no state law against multiple configurations of the weapon itself. Any local ordinances against it would be preempted by MI state law.