A method for retrofitting a downhole drill string with a flow through subassembly having a hollow outer body or barrel with a plurality of outwardly extending blades. Fluid flow inlets are provided in the lower section of the body below the blade openings and flow outlets are provided in an upper section above the blades. A fluid flow bypass channel is formed in the outer body and extends between said blades and from said fluid inlet to said fluid outlet. Drilling fluids outside of the subassembly may flow through the inlet, up the fluid flow bypass channel and out the outlet thereby bypassing any plug or pack-off formed between the subassembly and the well bore. Thus, an existing subassembly may be retrofitted to provide a fluid flow bypass channel around the blades.