If a lender adds charges, and retains the charge, to an item that would normally not be a finance charge doesn't the added charge become a finance charge?

Not necessairly.

I.e. from the OSC to 226.4(c)(7)(1)

. . . .In addition, the cost of verifying or confirming information connected to the item is also excluded. For example, credit report fees cover not only the cost of the report, but also the cost of verifying information in the report. In all cases, charges excluded under §226.4(c)(7) must be bona fide and reasonable.