Cash Shop Specials: 4/24 - 4/30

Actually, you can use Cubes and Bonus Potential Cubes on an item that is locked. I don't know if you would be able to use Potential Locks but I don't see why not.

I'm 90% sure my Dual bow was already locked when I was using potential locks to get 30% boss on first line while preserving 30% ignore defence on 3rd line.
I locked it for a year after scrolling last May, and finalized cubing later in the fall.