I feel your pain. If you only had created your pools before the (poorly overlooked) change was implemented in SCALE, you would have been spared from this irreversible issue. 
If it’s any consolation, @yorick created a feature request. We would love for you to vote on it. Hopefully iXsystems will realize how important it is to have this safeguard in place, which they already had for the longest time with FreeNAS, TrueNAS Core, and early versions of SCALE.