Oops!
You CAN mix kits in Style Mode, but only one at a time. E.g., one variation can use Standard, another one Ethnic. Or, alternatively, if you need just ONE hit from the ethnic kit while all other hits are silent (especially useful during a fill), you can embed a PC# in the middle of the variation or fill, then immediately next embed the PC# for the original kit (the arranger will switch VERY fast)...
It's not perfect, but can sometimes work...
More tips and tricks like this at Roland-arranger.com...
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An arranger is just a tool. What matters is what you build with it..!