They didn't look different to me. They played better. If you listen to the Chiefs after the game, they talked about how positive and upbeat they were during Halftime and how much it relaxed them.
Part of playcalling is the chess match. I don't think the Chiefs made any significant specific Halftime adjustments. I do think Reid found their rhythm and it took some time. Same effect, different mechanism.
You don't have time to draw up new plays, etc. but the playbook has far more plays than you actually run in a game, and you run a mix of defensive schemes, which gives you a lot of leeway to make adjustments. By half-time, you should have a feel for what's working and what's not, and someone should be scouting the opponent, especially with regard to what changes they may make in the second half.
Half-time does give the HC and coordinators time to talk with his assistants and decide what approach they want to take into the second half. During the game, things are happening too fast to fix anything more than the most egregious flaws.
The Eagles did a good job all season shutting down opposing offenses in the second half, but on the other hand, they've struggled against top 10 QBs both seasons, some because they're good and any defense would struggle, but also b/c I think Gannon runs a "play it safe' scheme which befuddles average offenses but allows top QBs to surgically pick them apart. Not sure how much is scheme and how much is lack of talent in the back seven that was covered up by a great pass rush.