It's not somehing I'd do without uprating the system with a relay & heavier gauge wiring... I have experienced the results when a previous owner did just that without mods & it melted my switchgear.
Also with the ST range unlike the Monster, when main beam is on, so is dip therefore you will be drawing about 180W instead of 115W meaning that the earth side for the headlamp needs up speccing and the drain on your charging system increases by over 150%......
HTH