If a consumer writes a statement specifically waiving their right to the three-day review is there a provision to allow for this?

The rule is quite clear on this so here it is:

Consumer's waiver of waiting period before consummation. If the consumer determines that the extension of credit is needed to meet a bona fide personal financial emergency, the consumer may modify or waive the three-business-day waiting period… after receiving the (Closing Disclosure). To modify or waive the waiting period, the consumer shall give the creditor a dated written statement that describes the emergency, specifically modifies or waives the waiting period, and bears the signature of all consumers who are primarily liable on the legal obligation. Printed forms for this purpose are prohibited. See 12 CFR 1026.19(f)(10)(iv).

 

It is important to remember that the definition of “consumer” under the Rule is limited to the borrower, as a consumer of credit. The seller is not considered a consumer under the Rule.

As a practical matter, lenders are unlikely to accept a waiver for a variety of reasons including instructions from the investor lined up to purchase the loan from the lender.