A washing machine appliance may include a tub, a basket, an impeller base, and an extended post. The impeller base may be rotatably mounted within the basket. The impeller base may include an impeller platform and a mounting face defined on the impeller platform. The mounting face may define a recessed cup. The extended post may be removably attached to the impeller base to rotate therewith. The extended post may define an interior cavity. The extended post may include a mating collar and an attachment piston. The mating collar may be on the bottom end in selective engagement with the mounting face at the recessed cup. The attachment piston may include a piston flange extending radially outward at an upper piston end and define an upper radial contact surface in selective engagement with a portion of an inner surface of the mating collar.