If your lights are all connected together leading to your existing switch then you cannot separate them unless you rewire the lights in groups of three... OR it may be more feasible to wire a Sonoff SV on each light so now you have full control of each light. You can then create scenes to control them in groups if you wish. If you put the Sonoff SV outside make sure it is in a water/moiture tight container and the WIFI signal can reach it. Also if you leave in a cold/hot area they may fail prematurely but at $5 it may very well be worth it.
Rob Dolata