Just to do a quick check, there isn’t a way to cancel transit if you made an oopsie on destination or method of transportation is there?
Nope, not currently.
dang it, thanks for getting back to me!
I had an oopsie like you mentioned last year and, on a hunch, I kept hitting the back button on my browser. It took me back to the Shipping page for the horse in question and I was able to ship it the way I had originally intended. It seemed to carry out the second shipping and not the first one, even though I did get charged for both shipping.
That’s a creative way to hack around a bug. 
For the record, that’s not intended use of the functionality, but if it works…