Can command make a soldier cancel an upcoming surgery due to training?

Short answer. Elective or cosmetic surgery; probably have to adjust around training or take leave. Doctor ordered surgery; you would be on profile with a surgery date and we wouldn't be having this conversation. That's what I've experienced.

To start, if you're eligible to reenlist, your command cannot choose when or how you reenlist, where you go, or when you leave. However, if you are not medically eligible to move your assignment will be canceled until you are cleared.
Your command cannot cancel your surgery for you, and unless it's an elective surgery they can't order you to cancel it yourself. However, they can take you to JRTC while you're recovering. It's not pretty, but it happens.
If you're told that you need to cancel your surgery, your best option is to go to IG and make an inquiry into the policy. If will inform you and the command of the correct course of action in your situation. Most if the times it's just an overzealous team leader or squad leader overstepping their bounds and they don't have the legal authority to order you to cancel a surgery, or even the backing of the commander. Commanders are rarely behind decisions that put undue hardship on their Soldiers.

I'm going to reenlist this Monday and PCS to a new duty station. I was going to set my PCS date to May so that I had time for my surgery and recovery, but since they're going to make me cancel my surgery so they can play the numbers games with JRTC, I see no reason to not just set my PCS date to April instead. I"ve never had a problem with my chain of command and certainly never had a problem big enough to have to use an open door policy, and I'm hesitant to even now unless I'm certain that I'm in the right when doing so. Can they make me cancel my surgery and can they decide when I can and can't PCS? Or is that something I can choose on my own without any command influence?