Firstly, I just want to say that I’m trying to make sure we build the right solution, so I’m sorry if I’m coming over annoyingly; that’s not my intention 
I understand what you’re saying, but my question is; Why was keg X assigned in the first place? The feature request looks to me to be asking for a solution to a problem that shouldn’t exist as the real mistake was assigning the wrong keg in the first place. Let’s fix the root cause, not stick a plaster on after the fact.
As I understand it, an analogy of where this feature request could be:
- I have a petrol car.
- I have put diesel in my car.
- Can my car please be modified to work with diesel?
- Instead, why not build a way to prevent diesel from going into a petrol car in the first place (like having two differently shaped pump heads).
Why was keg X assigned in the first place? Was this assigned because Allocate a beer batch (not a specific keg/cask) to an order at the point of ordering (in advance of assigning stock to the delivery) doesn’t exist yet?
Cheers