I just found out that I can add two different labels under the same label - that's pretty nice, since it cleans up the mouse-over legend. They even have the same color, so it's clear to see that they belong together.
However, I would still like to change the options of one of the series separately. Is this possible? E.g. can I access the series options via indices?
For example: I do have a theoretical function and some measured data points - they belong together, so they have both the label "Condition 1" (as an example). This works fine, but now I would like to have a different plotter for both (so that my function can show a line, and the measured points are drawn as points). Obviously I can not change the per series options via "Condition 1", since it would change both series.
Is it possible to still access them seperately, or do I have to set 2 separate labels?
No, you can't. The per-series options syntax won't allow this. To be honest, I'm surprised that having two series with the same name does anything sensible at all! If there's a behavior there, it's by accident, not by design.