In parkour gamemode there should be a command /reset for the Completed people because if people are completed many of my friends want to reset and a /reset command would be good for Completed Only When you use /reset command you get auto reset to level 1 and the command will only work with the people who have the Completed Rank on Parkour.
Neutral, if you go to level one and hit the sign at the end of it, it moves your rank back down to level two. Unlikely that the administrators would go out of their way for a command when you can essentially already do it.
Doesnt work for completed ranks, once youre completed you cant click any signs or demote yourself without opening a support ticket.