We can Hide/Expire Custom Field lookup items for any Lookup field under any module
by going to:
System -> Custom Fields -> Create and Maintain
Select the Section
Click on the Field you wish to hide/expire; and
Click the red X beside it
A new page will popup where we must check on Expire Action checkbox and click
Update to Expire that Value.
After clicking on 'Update', you must click on 'Save' for this to take effect.
After expiry, items can no longer be selected/viewed on Create page for that field. If we
want to Unexpire any expired value, we can do this by clicking the Blue Curvy Arrow next to
'Expired' items. The page will reload, and the value will be Unexpired.