No, you won't go to the back of the queue.
If youve changed to something out of stock it will means it could take longer though and it can delay it if you make lots of changes.
I like to think of it like being in the queue at [insert supermarket of choice here]. You have all your item bundled up in the trolley, or even already on the belt, at which point you realise you have picked up the wrong size can of cool whip and want to change it. Now, in this example, you may have an unwilling child in tow that can be sent back to change it, but you can actually tell the nice lady/gentleman at the till and they can send one of the shop minions (usually with retro 90s headset) to go and change it.
All the while you keep your place in the queue and go on your merry way with the correct configuration of your trolley
(I am fully aware this was an unnecessary analogy as Rakky had already answered the question, but even with this knowledge I shall somehow get through the day untroubled )