No, the only thing that you can do to change the combine mode of the chart is to set the CombineMode property on all series that you want to be combined. In your case you can set the CombineMode to Stack to all series and this should stack them. You can take a look at the Bar demo
that demonstrates RadCartesianChart and BarSeries with different CombineMode.
If this doesn't help it would be helpful if you can provide us with a runnable project (or code snippets) that demonstrates your implementation. This will help us in better understanding your scenario and assist you further.
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