Is a surety released if a contractor alters the specifications of a contract?

Hudson, at p. 810, says: “Where, however, the surety guarantees performance of a contract in terms which recognize in advance that the work under the contract may be varied (as is the case in most surety bonds for building contracts drafted at the present day), the surety is not discharged from his obligation on the ground of absence of notice of the variation, unless the party claiming under the bond had reason to believe that the adoption of the alterations would involve harmful results to the surety. So, the surety will be released if the plans are materially altered, unless power to alter them is expressly reserved in the building contract, and the mode of determining the alteration prescribed by the contract is substantially followed.” In United States v. Walsh (1902), 115 Federal Reporter 697, it was argued by the surety for the contractor that he was released from his obligation by changes and modifications made in the requirements of the contract by supplemental contracts made between the contractors and the government during the construction of a certain dry dock. The case was decided on this contractual provision: “ . . . and it is hereby further provided, and this contract is upon the express conditions, that the said plans and specifications shall not be changed in any respect, except upon the written order of the bureau of yards and docks; and that if at any time it shall be found advantageous or necessary to make any change, alteration, or modification in the aforesaid plans and specifications, such change, alteration, or modification must be agreed upon in writing by the parties to the contract, the agreement to set forth fully the reasons for such change, and the nature thereof, and the increased or diminished compensation, based upon the estimated actual cost thereof, which the contractor shall receive.” It was held that a surety for the performance by the contractor of a building contract, which provides that changes may be made in the plans and specifications by written agreement of the parties, is not discharged from liability by modifications so agreed upon which are not so extensive as to radically change the contract and substitute a different one.