Thanks for the reply. I had tried a few things...
on the Mac HD/Library/Arturia/Spark Dubstep/Spark Dubstep Library, I created folders inside the User Folder called Kit X/Audio/Drum1/Layer1. Then copied some drum samples into those folders. I hoped it might trick Spark Dubstep into loading the kit. No go.
My next idea was to take my sample and name it the same as a sample in the Factory folder and replace the original sample. I never got that far having decided to let Dubstep be Dubstep.
My brief l idea was mods ala Propellerheads ReBirth.