Once you merge two items, you can't
Situations where you can't merge an item
You can't combine more than two items at a time.
You can't combine items if both items have subitems. You must first
remove the subitems from the item you want remove.
Go to the Lists menu and choose Item List.
Right-click the item you don't want to use, and then click Edit
In the Edit Item window, change the item name to the same name
as the item you're combining it with.
Click Yes to confirm that you want to merge the two items
under the same name.
Other ways to remove an item
Change information about (edit) an item