Using a specific ticket in your MDX account.
(Setting the PRIORITY of multiple tickets.)
SAVING a NEW ticket in your MDX account for future use.
Many times a guest may have more than one valid ticket in her/his MDX account.
It can be very important to designate WHICH ticket will be used the next time(s) that guest
goes into a WDW park.
One way to do this is to make a stop at any Guest Relations outside any park (including Epcot's International Gateway) or at Downtown Disney's Guest Relations (called "The Welcome Center.")
Have the Guest Relations CM set the "priority" to the highest level of the ticket that you wish to use next at a park gate.
If that ticket has multiple assets (entries) on it,
it will stay set at the highest priority until its assets have all been used.
Some WDW Resort Concierge CMs can do this.
Stop be the Concierge desk and ask.
(If the CM there seems uncomfortable with the procedure, nicely decline the request
and head to a Guest Relations outside any park or visit the "Welcome Center" at Disney Springs.)
If you have a NEW (never been used) ticket that you wish to SAVE:
an easier way to accomplish this (with no need to make a trip to Guest Relations)
is to create a "fake name" profile in your MDX account and transfer that new, unused ticket to under that "fake" profile.
Since that "person" will not be going into a park, that ticket will never be used.
In the future, when you are ready to use (or upgrade) that saved ticket,
you can transfer it to yourself (or anyone else in or connected to your MDX account.)
You can even use that saved ticket's value toward renewing an (or buying a new) AP.