PRAAT provides a way: "Process-> Change formants...", but if I use Parselmouth call:
sound = call(sound0, "Change formants...", f1, f2, f3, f4, 0, 5000)
I get: "parselmouth.PraatError: Command "Change formants..." not available for given objects."
I really like Parselmouth, but I do wish more examples were available.