I think I just needed a good night of sleep. Here´s my solution:
base.buttonThrowers[0].node().setButtonDownEvent('button') #at class __init__
if curScene == 'Credits': #inside Task
self.accept( 'button', self.changeScene)
curScene = ''
def changeScene(self, key):
sceneFSM.request('Mmenu') #request to FSM main menu scene
self.ignore('button') #stop listening for "press any key" event, so this will only work if curscene = 'Credits'