You can modify the attributes of multiple projects in the Project Editor. Note that the PDFs of the projects you want to modify must be writable.
To modify the attributes of multiple projects at the same time:
In the Project Tree, checkmark all the projects whose attributes you want to modify.
Check out the PDFs of the checkmarked projects.
Choose Project > Attributes of Checkmarked Projects....
The Group Project Attributes dialog appears. See also Using the Group Project Attributes
dialog