Provided always, that nothing herein contained shall exclude any person or persons seized or possessed of a separate sheep walk or pasture of cattle in or over all or any of the common field lands in any parish or place, or in or over any part thereof, from using, exercising and enjoying such right in as full and ample manner, to all intents and purposes, as he might or could have enjoyed the same before the passing of this Act, unless such person or persons having such right as aforesaid shall consent or agree in writing at any meeting of occupiers, to be held as aforesaid, to a composition for the same or a limitation thereof, in which case every such consent and agreement shall be binding and conclusive upon every person so agreeing, and upon every other person coming to the possession of such sheep walk or pasture for cattle by descent or otherwise, until such time as the rules, orders and regulations for the cultivation of the said common field lands existing at the time of entering into such agreement shall expire.