Use if_ath.c for on the fly transmission power change?

[Sam Pierson]

I was curious if there was a way to use the if_ath.c file in order to change
transmission power on the fly in the middle of a program.   This is in if_ath:

  ath_hal_setuptxdesc(ah, ds
                , pktlen                /* packet length */
                , hdrlen                /* header length */
                , atype                 /* Atheros packet type */
                , 0x60                  /* txpower XXX */
                , txrate, 1+10          /* series 0 rate/tries */
                , iswep ? sc->sc_ic.ic_wep_txkey : HAL_TXKEYIX_INVALID
                , antenna               /* antenna mode */
                , flags                 /* flags */
                , ctsrate               /* rts/cts rate */
                , ctsduration           /* rts/cts duration */
        );

So I would assume there is a way to do it, although I seem stuck.  Do I have
to construct each packet by hand (is this even feasible)?  I saw back in 
September that Sam Leffler said "per-packet TPC is not working right now", 
so I assume that it may have been worked on or at least checked out since 
then.

Thanks