I just got my MT this morning: yes it is possible to recalibrate the speedo for 2010 DX: this does not appear in the ECM constant menu, but just before reflashing the map.
There's a VSS calculator (I attached a screen capture) that will calculate the VSS "value" for the various HD models with selectable tire sizes and sprockets. This calculated VSS "value" is entered during the programming process to calibrate the speedometer as "bpf" mentioned.Does the retuning allow you to change wheel size, or just sprocket sizes?