Meh, I f the government upped the MSO from 8 years to 12, THAT would be a change to contract after it's signed.
While I love the 90 days boots-on-ground policy, anyone who joins thinking that policy is permanent needs to re-visit what the word "policy" means. In my ASR hat, I was very explicit to folks that the 90 day deployment could change with the swipe of a pen, and if that was a deal-killer, they should NOT join. I banged that drum in more than a few postings on this forum.
It's not a bait and switch. The Army needed a boatload of docs during a heavy tempo war. The tempo slowed down, so they're changing a policy that likely accounted for a lot of reservists joining. I think it's a poor decision, because it seems like the military is going to be more reliant on reserve corps in the decades to come, but there you go.