This post is a revise to my last one, I see that in the v.12 upgrade, we have a new type called Will Call 2. The category of it is Ticket, and was attempting to use it as an example for a Header. Can it be changed to a header?
When you are in the Ticket Design List screen, the Category specifies which dropdown list the design will appear in -- MOS setup for headers, Paymethod setup for receipts, or Pricing tab on performance setup for tickets.
You can edit the Category for a design by selecting it and clicking the "Edit" button -- the category column will turn into a dropdown. If you do this, you will want to make sure that all of the elements contained on the ticket design are allowed for the chosen category. The element types allowed for each category are listed on this page of documentation ("Used In" column).
If you just want to test print a ticket design, you can do that easily from the setup module by double-clicking the ticket design (or clicking "Edit Selected Design") and using the "Print Sample Ticket" function in the toolbox. The data populated in the ticket will be whatever is in the T_DESIGN_ELEMENT system table (Test Val column).