I am afraid there is no way to use the specific calendar since the uxdat doesn't accept MU as argument.
Sorry, I can't be more helpful
An update to this topic.
One of our product expert has just told me that the uxdat does accept MU as argument in fact. Since this info is not documented, a doc enhancement has been opened.
So the command should look like this:
uxdat "mm/dd/yyyy" "01/01/2014" "type" [MU=<MU name>]