eg. I am plotting waveforms like ac response for different values of load capacitance, how to get all the plots in a single waveform to show the variations?
You can also simulated your design without any outputs to plot. Then you go to "Virtuoso Analog Design Environment" -> Results -> Direct Plot -> Main Form and on the "Plotting Mode" you choose "Append" and plot the value you want. This way you can simulate and plot multiple times without loosing the previous plots.
Another way for doing this, is to export the plots data each time in tables and after you collect all the data you can plot the figure as you wish in excel or matlab....