10. (1) The court by which a probation order is made under section 5 may at any time, on the application of the person under probation or of the probation officer or of its own motion, if it thinks it expedient to vary the bond taken under that section, summon the person under probation to appear before it, and, after giving him a reasonable opportunity of showing cause why the bond should not be varied, vary the bond by extending or reducing the duration thereof or by altering any other of its terms and conditions or by inserting additional conditions therein: Provided that in no case shall the duration of the bond be less than one year or more than three years from the date of the original order: Provided further that where the bond is with surety or sureties, no variation shall be made in the bond without the consent of the surety or sureties; and if the surety or sureties do not consent to the variation, the court shall require the person under probation to execute a fresh bond, with or without sureties. (2) Any such court as aforesaid may, on the application of any person under probation or of the probation officer or of its own motion, if satisfied that the conduct of the person under probation has been satisfactory as to render it unnecessary to keep him under supervision, discharge the probation order and the bond.