I think you have to distinguish the "rush fee" from the "appraisal fee." A lender can't add an appraisal fee to the costs to be borne by the borrower if the lender forgot to include the fee on the initial loan estimate. You cannot fix mistakes like omitting a fee that the lender should know will apply based on industry practice, etc.
So, the bank is stuck with the basic appraisal fee, but I think it could add the "Rush appraisal fee" to the extent that it's an "add-on" to the basic appraisal cost that the bank should have included on the original loan estimate. But it only has three business days from learning of the need for the rush appraisal fee to get the revised loan estimate out.
John S. Burnett
Fighting for Compliance since 1976
Bankers' Threads User #8