It is possible to name multiple plots using the Plot Name property, however it must be used in conjunction with the Active Plot property.Figure 1.
Change Multiple Plot Names (VI Snippet)
The Active Plot property effectively specifies the index of the plot which you can change the properties for the specified plot.
Another useful property for such applications is the Legend Number of Rows, this will then auto-size the legend according to the number of plots displayed by the Chart.Figure 2.
Change Multiple Plot Names