I believe you should be able to use a second wax ring to make up for the additional hieght of the new floor.
Phil : i replacing my bathroom floor...have added a new sub floor of 1/4 inch plywood and 1/2 inch cement : backerboard....then will be adding ceramic tile, which : leaves my closet/floor flange below floor level, how do : i replace/extend that flange...do i remove the old one and add a new one, or is this something that i can add onto....is there a kit?