One of the trip wires for flood is an 'extension'. I feel confident that this does not apply to a monthly payment deferral, but need some help finding the documented support of this. Can someone direct me?

"Extension" refers to any change to the legal obligation. For example, if you re-amortize the loan to reduce payments or agree to extend a deadline or maturity date, it would be an extension. Allowing the customer to make a late payment would not be an extension. And you should be covered for flood insurance purposes already -- if you have been in compliance.