But I still wonder how he will get through his residency. Can they actually choose a specialty for their residency? I thought they had to put in their time in different rotations?
That's basically what residency is - they've done all the mandatory schooling, including exploring the various specialty areas, and are actually working in their chosen specialty. In my area, for example, OB/GYN is 6 years' residency program, and they sign their names along with the level (R1, R2, etc. up to R6) when they write orders, so we know when someone is a "junior resident" as opposed to a "senior resident", and we can go up the chain of command if we need to question anything or disagree with an order from a junior resident. The junior resident is expected to consult with senior residents or staff doctors if they find it necessary to do so, and the "staff man" is considered the final authority.
What Snakes said is correct - a JW physician-in-training (residency) can get away with ordering blood transfusions by referring back on the chain of authority standard. BTW, pain management would be a really $$$$weet $$$$pecialty to get into.