Section 49I. (a) The security required under section forty-nine D shall be cash or securities permissible under state law as security for deposit of state funds and in such amount as the commission may require but in no case in excess of the limits specified in section forty-nine E in reference to the limits of a policy or bond. If at the time of the accident there is in effect a liability policy or a bond meeting the requisites of section forty-nine E other than the amount of coverage set forth in said section, the commission may consider such policy or bond in fixing the amount of security. The person depositing security shall specify in writing the person or persons on whose behalf the deposit is made and, at any time while such deposit is in the custody of the state treasurer the person depositing it may, upon approval of the commission, amend in writing the specification of the person or persons on whose behalf the deposit is made to include an additional person or persons; provided, however, that a single deposit of security shall be applicable only on behalf of persons required to furnish security because of the same accident. Interest and other income upon securities deposited as herein provided shall be paid or inure to the benefit of the person making the deposit.
(b) Upon ten days' notice of the parties concerned, the commission may reduce, or, within the limits specified in section forty-nine E, increase the amount of security ordered in any case if in its discretion the amount ordered is excessive or insufficient. In case the security originally ordered has been deposited, the excess shall be returned to the depositor notwithstanding the provisions of section forty-nine J. Substitution of security shall be permitted.