I guess that would be an action like "Randomize pitch", then set the range like 0.6 to 1.4?
Though that's exactly what "Set Playback Rate" does and it's only 1 action, too. Can throw in random(0.6, 1.4), or if only specific pitches, choose(0.6, 0.8, 1, 1.2).
AFAIK pitch alone doesn't change the sound speed, at least it didn't when I checked in Audacity. Probably it's the same for other audio editors. Javascript audio doesn't let you change pitch however, only the playback rate, so i doubt it's possible in construct.