I don't understand why you want to rename the mediator, which actor would invoke the renaming and when you'd be doing it.
i check facade.hasMediator(<id of the document>) which returns false
This tells me that you either...
1) failed to supply the id of the document in the call to super in your mediator subclass' constructor,
2) you created the name differently when the mediator was registered than when you check for it,
3) the id you have in hand when you're calling facade.hasMediator(<id of the document>) is not correct.
4) the mediator has already been removed by the time you're calling facade.hasMediator(<id of the document>)
If you register a mediator with a given name, facade.hasMediator will always return true if you supply it the name the mediator was registered with AND it hasn't been removed.