Section 7. Any person, or the agent of any person, owning an estate abutting on any sidewalk as aforesaid, may, on or before November first in any year, procure the exemption of such estate from the assessment aforesaid for the following year by a stipulation in writing with the selectmen that he will remove snow and ice from the sidewalk on which the estate abuts, at such time and in such manner as the selectmen or road commissioners shall direct; and if he fails to fulfil his stipulation the assessment above provided for shall be made and collected as if no such stipulation had been made.