Idaho Code § 19-1420: Amendment of indictment.

An indictment or information may be amended by the prosecuting attorney without leave of the court, at any time before the defendant pleads, and at any time thereafter, in the discretion of the court, where it can be done without prejudice to the substantial rights of the defendant. An information or indictment cannot be amended so as to charge an offense other than that for which the defendant has been held to answer.