Since your E-6 film is basically 3 different color layers, anything you do to mess with the 1st developer will end up developing the layers different from standard and cause color shifts. There are times for pushing and pulling. I fiddled with trying to control harsh contrast scenes by over exposing, under developing very similar to B&W. Mostly its a good way to burn up time and $$. Similar to a Harley D turning gasoline into noise.