Grant variances from the strict application of this chapter when, by reason of exceptional narrowness, shallowness, shape or topography of specific parcels of property at the time of the original enactment of this chapter or amendments, or where the strict application of this chapter or amendments would result in exceptional or undue hardship upon a property; provided, however, that such relief of variances can be granted without substantial impairment of the intent or purpose of this chapter. This subsection shall not be construed to permit the Board, under the guise of a variance, to change the uses of land.