I never ended up doing this, so no worries on that part. Its crazy though, because when you Google sour crop, 99% of anything I found said to do this and not much else.
I have heard of chickens aspirating when they are forced to vomit and that can be fatal (plus is a horrid way to die). Then again forcing anything to vomit carries that risk since they are not in control of it.
Not saying this applies to you, but it does seem there are a lot of chicken keepers that don't have the sense God gave a turnip when it comes to these things.