Diebold May 23 1871 Combination Lock Change Key

[Kevin11]

I have a safe which has an outer door with a 1871 diebold 3-wheel pack combination lock, and also has an inner door with a 1871 diebold combination lock which has a 4-wheel pack.

I noticed that both combination locks wheel packs have what appears to be a special 'square' hole that goes through the front of the lock body, then into each wheel, and then continues out through the cover. The 'square' hole has 3 square sides and one corner which is mitered/beveled. I set the lock to open and noticed that it looks like all of the holes will line up with each other when put in the sequence as if something was made to be slid into them.

I have read where lock manufactures made change keys for their locks. Is this hole for a change key? If so, how does it work in detail for this particular diebold lock? Is a change key necessary to reset the combination? Instead of making a change key even though I have access to a machine shop, where can I find and buy one?