modifying pdf of a GMM using gmdistribution

I have made a GMM using gmdistribution.fit on a dataset and now I'd like to alter the PDF by making the highs higher and the lows lower, for example by squaring or cubing the individual pdf values and then renormalizing so it sums to 1. The point is to emphasize the peaks of the distribution even more when sampling from the gmm. How can I transform the gmm in this way? Thanks!

Gene

[Eugene Kogan]

An alternative method would be constructing my own arbitrary pdf... how would you go about sampling from an arbitrary probability distribution. I prefer the first way as long as its possible to shape/modify the pdf somehow.