Allow editing PM after creating it to make it a warning

[tobiaseigen]

I see this has come up previously:

Proposal: Undo Official Warning

Hi all, I’d like something like this: Undo an Official Warning But from the front end. Perhaps the checkbox that is used to designate a PM as a warning, can be exposed to an administrator when they edit the warning PM in question, and it could just be a matter of undoing the check.