You can try and interact/play with the browser history using window.history.pushState but in my experience it's a little inconsistent and if a user keeps clicking back then they still might get back. My suggestion would be to actually modify the code page and before you do anything check to see if that record has already been processed like checking a box for 'copied' on the original record. Another option is to provide a submission screen where they user can cancel out to cancel (like a confirm/submit & cancel buttons page instead of having the code page automatically process).
\In the first example where you check to see if you should copy - you can instead just redirect them to the home page since they've already processed that entry.
