help with lighting effect

So the show is next weekend and now during a scene they want a lighting effect just on some lights in the back row (channels 401-403).  I have learned how to do a liner effect with a "heart monitor" design to give kinda the effect (not great but mine is ok I guess).  Now how do I have the stage lights on and then just those few lights do a lightning effect during a cue?  

Can I make them a group with the effect and somehow put it to a submaster fader so I can do it whenever the director wants it?  Do the lights have to be off before hand to get the effect?  Currently they are on in the cue he wants to see the lighting happen (at 2 different times).

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