Some more details about your project may help us answer your question. Are you trying to add labels to multiple plots on a single chart or simply add labels to the plot legend?
Using property nodes is a good idea, but right now your code is changing the plot name for every plot each time the chart is updated--this is likely redundant. What sort of behavior are you observing with your code right now?
We may be able to offer more specific advice if you can provide a smaller section of code which demonstrates your question.