Any structure or use of structure which is modified such that the sewer impact assessment is greater than the amount for which the initial impact fee was computed, the owner shall be assessed additional impact fees in accordance with section 78-121. For any change of use which increases the original impact fee for which the building was constructed, the owner will be assessed additional impact fees in accordance with section 78-121. For any change of similar use which increases the number of units (per seat, per worker, per square feet of floor space, etc.) within the establishment, the owner will be assessed impact fees only on the additional number of units proposed to be constructed, in accordance with section 78-121.