Why would page level locking be disabled on an Index?
By default, [allow_page_locks] is set to 1, so, someone must have changed it in the past to avoid that level of locking.
If I go ahead and make changes and allow page level locking, it is not going to break anything, right?
I would test this in a non-prod environment prior to changing. I would think the outcome would be unexpected locking.
Is there a script?
You could use this script to identify those indexes and then change it to modify those. But, I would think there was probably a good reason for the change in the first place.
from sys.indexes Indx
left outer join sys.objects OBJ
where allow_page_locks = 0