I’d done this some time ago. My RE portion sat before my main partition - and since you can’t shrink partitions at their start (left) with fdisk and I didn’t want to boot up a Linux pen drive, I just shrank the main partition at its end (right) and moved my RE partition to the end.

I’ve made the now free partition available, but since it’s just a few hundred MB, I doubt I’ll ever actually use it. :-P