The amount of the bond or deposit required and the terms of acceptance of the applicant's bond or substitute collateral may be increased or decreased from time to time to reflect changes in the cost of future reclamation of land mined or to be mined. The amount of the bond or substitute collateral may be reduced only in accordance with the provisions of the following §11.206 of this title (relating to Release or Reduction of Bonds) and such bond or deposit shall be increased or decreased when actual acreage affected by mining is ascertained.