Well, there's actually a few steps to it.
First, open your ROM in a move editor and swap the positions of Rock Climb and the HM you wanna replace. That will do the hard work for the blue party option thing.
Second, you have to add tiles that will react to Rock Climb. XSE for the script, like Surf or Waterfall scripts. Insert somewhere in the ROM and somehow (which I don't know yet), make the tile react to Rock Climb (one idea for this is having it show up as an event, which would be much easier to make it react to Rock Climb, but more poorly made, in my opinion).
Third, you have to edit the blue party option. Altough your attack is shown Rock Climb, the effect stills the same from the HM you have replaced. Right now, your Rock Climb is working perfectly, but only for this detail. It will work as the previous HM until you make a routine for calling Rock Climb from the menu, and then repointing it here. Follow this:
http://www.pokecommunity.com/showpost.php?p=8676227&postcount=530
After all this, Rock Climb is working perfectly.