To change. Alterations are made either in the contract itself, or in the instrument which is evidence of it. The contract may at any time be altered with the consent of the parties, and the alteration may be either in writing or not in writing.
It is a general rule that the terms of a contract under seal, cannot be changed by a parol agreement. But it has been decided that an alteration of a contract by specialty, made by parol, makes it all parol.
When the contract is, in writing, but not under seal, it may be varied by parol, and the whole will make but one agreement.
When the contract is evidenced by a specialty, and it is altered by parol, the whole will be considered as a parol agreement.
An act done upon an instrument in writing by a party entitled under it, without the consent of the other party, by which its meaning or language is changed; it imports some fraud or design on the part of him who made it. This differs from spoliation, which is the mutilation of the instrument by the act of a stranger.
When an alteration has a tendency to mislead, by so changing the character of the instrument, it renders it void; but if the change has not such tendency, it will not be considered an alteration.
A spoliation, on the contrary, will not affect the legal character of the instrument, so long as the original writing remains legible; and, if it be a deed, any trace of the seal remains.