This section is from the book "The Law Of Contracts", by William Herbert Page. Also available from Amazon: Commercial Contracts: A Practical Guide to Deals, Contracts, Agreements and Promises.
Only the party who is apparently liable on the contract as altered can complain of the alteration. The party who makes the alteration cannot treat the contract as discharged if the adversary party seeks to enforce it.1 Third persons cannot complain of such alteration if both parties to the contract acquiesce therein. So if an insurance company does not raise objection to an alteration in an insurance policy changing the beneficiary from the insured's "estate " to his "wife and children," his creditors cannot complain.2