Cam we have a custom recipie to turn created maps back into blank maps. This could be done using Blaze powder (used to undye glass/unstick pistons) and a map with any saved Id. I'm sure a lot of players have maps that were created with missing pixles or made in bulk a few too many copies to sell, or wish to reuse old irrelevant maps. This could be a great idea to support this suggestion.
Support! The number of times I have accidentally locked a mapart without realising that I missed a few pixels on the edge is embarrassing at this point, and I usually end up voiding them.
Bump... I have started a chest of maparts I have accidentally made/locked in anticipation of this being implemented.
