No obliteration, interlineation or other alteration made in any unprivileged will after the execution thereof shall have any effect, except so far as the words or meaning of the will have been thereby rendered illegible or undiscernible, unless such alteration has been executed in like manner as hereinbefore is required for the execution of the will:

Provided that the will, as so altered, shall be deemed to be duly executed if the signature of the testator and the subscription of the witnesses is made in the margin or on some other part of the will opposite or near to such alteration, or at the foot or end of or opposite to a memorandum referring to such alteration, and written at the end or some other part of the will.