hPlot = plot( hAxes, [0:0.1:2*pi] , cos ([0:0.1:2*pi] );
will plot on the axes specified by hAxes (which can be acquired easily whether you are using GUIDE or just creating the axes as you go) and return the handle to the Line object of the plot in hPlot.
You can then use, e.g
set( hPlot, 'XData', 0:0.1:4*pi, 'YData', cos ([0:0.1:4*pi]) )
That is just a quick example. Personally I would factor the common 0:0.1:4*pi out into a variable, but I was following your example here!
I'm not sure what happens if you just do:
hPlot.XData = 0:0.1:4*pi;
in this case. You have to be careful when changing a property which effects others too as in a line plot it is expected that XData and YData are the same length so changing just one to a different length presumably results in a bug. I haven't tried it.
I'm not 100% clear exactly what your question was though since you talk about list boxes too, but don't appear to be asking about those.