Let's say that you wanted to render a certain scene in Revit, and then save the resultant image to the Project (a Central File). As this render could take 10 minutes, you want to keep working on something useful in the same Central File. What to do?
You just need to open a new instance of Revit and change the Username, then open a Local Copy of the Central as per usual. You now have 2 instances of the same Central model open, and you can work in and Synchronize from both of them ... obviously you are going to need some decent hardware if you are working on a large central file with links. Set the first instance to render, and work in the second instance while that is happening (keep in mind that local renders in Revit can use multiple cores, so you may want to think about manually adjusting core affinity).
The username can be changed in the Revit Options dialog:
From Steve's post:
You can however change your username anytime you want when you work in a central file. It isn't a great idea to actually work this way, switching usernames as you go. It is however a way to clear out users that have not relinquished worksets properly though. When nobody else is working on the project you can open a central file and pretend to be the ill mannered users that haven't relinquished elements properly. It's another reason you might consider working in a central file, even though it is generally frowned upon.
Read more at:
Revit OpEd: Changing a Username