Soon I will be transfering my koi to a new and larger pond. They seem
healthy right now, but since I'm going to have to capture them and put
them into a small container to adjust them to the water in the new pond
I was considering using this as a chance to give them a salt bath too.

I was considering this, after they've adjusted to the water conditions
of the new pond while sitting in their small container/bag of old water
I would add salt at the rate of 1lb per 5 gallons of water. Then I'd
let them sit for up to five additional minutes (or until they start
rolling over) then I would release them into the new pond.

I think this seems like a great chance to do some preventative
medicine, but would the stress of the salt bath and the adjustment to a
new pond be too much stress for a koi to endure?

(If it matters, the koi are roughly 14"-18" in length. One is a
butterfly koi and the other 7 are regular koi)