The holder of any such certificate of public convenience and necessity for the operation of an autobus heretofore granted and now in effect or hereafter granted and in effect may replace any autobus operated under such certificate of public convenience and necessity with another autobus and may substitute one autobus for another and may operate such other or substituted autobus under such certificate of public convenience and necessity provided such other or substituted autobus shall conform with lawful regulations and specifications.
N.J.S. § 48:4-8