This situation came up yesterday. Hand ends and the BTN is on seat 2. Player in seat 2 has a seat change btn and the player in seat 7 asks for a seat change btn as well. Seat 2 asks if he wants to switch and he agrees. They switch seats and the dealer calls the floor to get clarification on how to handle this. Floor says that the guy that moved from 7 to 2 can't move to the btn so must wait a hand. Guy who moved from 2 to 7 must post because he moved more than 2 seats. Player argues that he is moving away from the btn and giving up position so he should not have to post. Floor seems a little confused as to the rule but ultimately decides he must post. Player gets angry, racks up and leaves. I'm sure card rooms can set their own policies on this, but what so you guys think?

It is going to depend specifically on the rules in this specific poker room.

In many (not all) poker rooms, when two players exchange seats, it has no impact on the other players' positions or blinds posted, so play simply resumes with nobody posting anything extra.

If he's moving to a seat where he will pay the blinds later, he should have to post. But if someone is moving out of the button, he will get the blinds sooner than he would have at his old seat, so he should not have to post (in almost all rooms). I did play one time in one room where anyone moving had to post, even if they were moving towards the blinds, but that is extremely unusual.