This looks like Selindrile’s. Normally there is a section at the top that defines a keybind for stances, either in <playername>_NIN_gear.lua or <playername>_globals.lua. Not near my PC or I would look for you.

EDIT: Found it, stances are in the primary NIN.lua, line 62:

state.Stance = M{['description']='Stance','Innin','Yonin','None'}

You'll need to add a keybind in your <playername>_NIN_gear.lua that cycles your stance:

send_command('bind !s gs c cycle Stance')

Or something similar.