Is it possible to use stringoverride on ONLY one page?
I'm betting you're looking for hook_form_alter() ... I'm pretty sure its just a form buttom on the page and you can change its #valueproperty as-needed with that hook. Its up to you to figure out how to target just that form, on just that page ... I don't think you need stringoverride for this.

You would want to test this out of course :)