editing legend of Spectrum Analyzer output

Hello, I am trying to simulate a matlab function block of my main Simulink model which displays Spectrum of signals. My code creates an object of dsp.SpectrumAnalyzer function and the output is obtained using the corresponding step method of spectrum analyzer. Since I am using the 2013a version of Matlab there is no option to edit the channel names displayed in legend and I could edit it only in the Spectrum window output directly. I cant use the spectrumanalyzer block due to my code being dependent on various parameters and the number of spectrum plot may vary. Please suggest a workaround for this as soon as possible.