Provide exemption for certain modifications to residential property

This bill creates a property tax exemption for homeowners who modify their existing residential structures to add living space. It directly affects owners of class four residential property who make changes like expanding a building or altering its form. The exemption allows owners to exclude the lesser of the increase in market value caused by the modification or 15% of the property's prior year market value from their property tax calculation. The exemption is automatically granted by the department of revenue, but it cannot be claimed for properties built within the last three years, is limited to once every six years per property, and ends when the property is sold. The changes apply to tax years beginning after December 31, 2025.