In Expiration Reminder there's an option to archive an expiration instead of deleting it. Deleting it an expiration will remove it from the system and it won't show up anymore while archiving will still show up in the system but will be read only and won't generate any notifications.
Archived is also a status that can be changed using the Change Status dialog.
Archiving an expiration
For the expiration that's going to be archived, click on the drop down menu with the black arrow and then click on Change Status.
From the status list, select Archive:
Once an expiration is archived, the status will change to gray:
Unarchiving an expiration
For the expiration that's going to be unarchived, click on the drop down menu with the black arrow and then click on Change Status.
From the status list, select Unarchive:
After unarchiving, the system will automatically calculate the current status: Notify, Expired or Notify.