You can create new XSLT parameter set or modify an existing one. To do this, open XSLT Parameter Set Dialog: :
Figure 1. XSLT Parameter Sets Dialog
Note, that not every top-level XSLT parameter is shown in the dialog. In order to be present, it should have se:type extension parameter. See Specifying XSLT Parameters for Parameter Sets.
If you wish to save changes in XSLT Parameter Sets go to
to save your changes either for the current document or the template. If you forgot to save the changes and closed the document, then open document from Recent File List: your changes will be restored for this document.