All you need is:
{IF{Mergefield Selected_Product_Frequency}<> "Bi-Weekly" "Late Charge: If a payment is {IF{Mergefield Opportunity_Borrower_Type}= "Refinance" "late by more than 15 days, you shall be subject to a late fee of $15.00." {IF{Mergefield Opportunity_State}= "SC" "15 days late, you will be charged $18.00 or 5% of the unpaid payment amount (A minimum of $7.20 and a maximum of $18.00)." {IF{Mergefield Opportunity_State}= "NM" "15 days late, you will be charged the lesser of $10.00 or 5% of the unpaid payment amount." {IF{Mergefield Opportunity_State}= "TX" "late by more than 10 days, you may be charged the greater of 5% of the delinquent installment amount or $7.50." "late by more than 15 days, you shall be subject to a late fee of $15.00."}}}}"}

The added part is shown in red.

Note: You don't need any of the Mergeformat switches; they add nothing useful to the process. I've also simplified the rest of your field coding somewhat.

__________________
Cheers,
Paul Edstein
[Fmr MS MVP - Word]