What will you do with the CAL file?
I guess if I know what you are trying to achieve I can maybe answer the question better. A CAL File is actually pretty much the same as a DC file, however the CAL contains more information than e.g. an SCS900 DC file.
So in some cases you could simply rename the DC file output as a part of an SCS900 Site to a .CAL and it may do what you want, however if you start off with a project with just a Coordinate System and Datum then using the CAL file in e.g. SCS900 would allow you to use the Coordinate System information and then do site calibration on top to localize.
However if you have all the GNSS and Local Coordinates in the project and want to write out a CAL file and then use SCS900 to analyze the residuals and create a Site Calibration DC file without doing any observation, I dont believe that is possible.
So let me know what workflow you are trying to satisfy by writing out a CAL file and I will try to give you some direction here.
Alan