Yes. When aftermarket equipment is attached to qualified farm machinery or equipment it becomes an existing component of the qualified machinery or equipment. Therefore, replacement parts for the aftermarket equipment that had previously been attached to qualifying machinery or equipment, and any installation charges for those replacement parts, are exempt from sales tax.
For example: A farmer purchases an air conditioning unit to be placed on qualifying farm machinery. The initial purchase of the air conditioning unit is subject to sales or use tax. Once the air conditioning unit is attached and becomes a component part of a qualifying piece of farm machinery, replacement parts for the air conditioning unit, and installation charges for those parts, are exempt from sales and use tax.