Here's an excert from a FDIC FIL dated July 31, 1997. This memo is actually written by the FFIEC, this is just the FDIC's copy of it.
4. Section 528 of the Act permits a lender to rely on a previous determination using the SFHDF when it is increasing, extending, renewing or purchasing a loan secured by a building or a mobile home. The Act omits the ``making'' of a loan as a permissible event to rely on a previous determination. May a lender rely on a previous determination for a refinancing or assumption of a loan?Answer: It depends. If a subsequent loan involving a refinancing or assumption is made on the same property by the same lender who obtained the original determination, and the other requirements contained in Section 528 are met, the lender may rely on the previous determination. Section 528 of the Act requires that a lender may rely on a previous determination only if the original determination was recorded on the SFHDF within the previous seven years and there were no map revisions or updates affecting the security property since the original determination was made. However, a loan refinancing or assumption made by a lender other than the lender who obtained the original determination would constitute ``making'' a new loan, thereby requiring a new determination.
Therefore, I think that if you already have a determination for the property you do not have to do a new determination. Same property and same lender = no new determination.
If you do not perform a new determination, do not charge the borrower. If you do perform a determination, you can (but you don't have to) charge the borrower.