After the provisional order hearing and at the time of the passage of the ordinance creating any improvement district and any projects for the improvement district, or any amendment thereof, if any tract or any railway company to be assessed in the improvement district has the whole or any part of the proposed projects, conforming to the general plan, the same may be adopted in whole or in part, or may be changed to conform to the general plan, if deemed practical, and the owner of such real estate shall, when the assessment is made, be credited with the amount which is saved by reason of adapting or adopting such existing improvements.