I'm somewhat new to this as well, bit i've done it. Let me see if I remember correctly.
1- D/L and install RR skin editor
2- Open your skin
3- Go to the page in the skin that has the button you want to change (I assume the menu)
4- Right-click on the button's area and change the action from RADIO to LAUNCH, then add a space then the path to the executable you want to run.
I may be a little off, but that's generally how you do it if i'm remembering correctly. Hope I could help.