I think you're probably overestimating the portability of IP addresses, and underestimating the coercive power of the organization that does the seize.

IP addresses are assigned to a network provider, not a customer. If I'm hosted by a US provider and the FBI seizes my server, is that provider going to say "sure, just spin up a new box on the old IP", or are they going to tell me to get off their network? What if the FBI has an opinion on which decision the provider should take? What if the FBI has an opinion on which action the directory operator should take?