You can indeed use Grub to boot once only. You can also specify a fallback boot. Essentially, you use default saved at the start of your grub.conf, to indicate that you want to boot a saved entry by default. Then at the end of your experimental boot, use savedefault # to set the older boot options as the new saved value. So that every time you boot the new kernel, grub saves the older one as the next boot.
Lastly, you can always do your test as a manual boot, if you can access the Grub loader. That way, a reboot will always use your original default.