In the ITP Model, you can see these instructions:
(* Set style document *)
#@(stylesheet(label; document_type))#
The result of the function stylesheet is produced as output in the result document. Again, the variables document_type and label are used as parameters. Calling the function creates a reference to the template document with Microsoft Word styles in the result document.
Since only one set of styles is available in a Microsoft Word document, it is only possible to have one style sheet per model run. For more information refer to the model developer's Help topic stylesheets.