If the Commissioners do not fix such "Level within Six Weeks from the Time of the Delivery of such Notice as aforesaid, unless the fixing of such Level be delayed by the Appeal herein-after provided, the Person giving such Notice may proceed to lay out the Street at any Level which will allow of Compliance with the other Provisions of this and the special Act, as if such Level had been fixed by the Commissioners ; arid in such Case every Change of the Level which the Commissioners afterwards deem requisite, and the Works consequent thereon, shall be made by the Commissioners, arid the Expence thereof) and any Damage which any Person sustains in consequence of such Alteration, shall be defrayed by them.