The parameters of the shipped Taks Performers are explained at SDK Docs.
And, copied from that link:
The placeholders recognized in file names are:
[extension]. Replaced with the extension defined in the target language's .language file. Used to specify code file extensions.
[time]. Replaced with the actual current time in the format: yyyyMMdd-HHmmss
[containerName]. Replaced with the ActiveSourceElementsContainerName value of the executing Generator object, which is the projectname when the project property GroupUsage is set to AsVisualGroupingMechanism, otherwise it's the active group name.
[elementName]. Replaced with the name of the element, e.g. the name of the current entity.
So: no, you can't use the root namespace as part of the fileName in the CodeEmitter task performer. The ProjectFileCreator task performes does recognize additional placeHolders. So if you really want that, you should write your own task performer for that.