I can speak to this somewhat, although not really - I'm still into some really extreme shit. However, if it ameliorates the issue at all (and it may not), today I feel as if I have more control over what I consume than when I was younger.
In my youth, I consumed it all. Anything and everything, without regard to whether it was right or wrong. The only limitation was no gay shit. But even that's debatable as traps and shemales are considered gay by some, though not by me. And while I am 100% correct on that topic and they're all wrong because they're dumb and stupid (and filled with poop, they have poop inside of them), I digress.
Today, my fetishes include even more extreme content than back then, but that extreme content is enjoyed rarely and never too much. I've naturally kept it to a minimum to avoid polluting my rotten mind any further, and it's worked to some extent. I have found that it hasn't affected my regular life or even my enjoyment of ordinary porn at all. I never "have" to fap to it. In fact, often times it's simply so rare that I must collect it. Sometimes, I do enjoy it. It is what it is.
One of the keys, I think, is to have a rock solid mental barrier. If you can easily and thoroughly compartmentalize, it's much less of an issue if at all. Now, you're never going to get rid of that stray or intrusive thought or daydream, and that can be a minor issue since if you never consumed that kind of content, you'd never think about it even in passing. But, it's something you get used to, just like every other random thing that pops into your head. Simply dismiss it and don't let it perturb you.
On another note, willpower is unreliable. It diminishes rapidly and recovers slowly. Discipline and normal, human interaction is vital to ensuring that the part of your organic harddrive dedicated to sick porn doesn't escape and fill in space that would otherwise be empty. So, in short, crunch that shit into a small space, and fill the rest of your brain up with normal stuff. The higher the ratio of normalcy to degeneracy, the better off you will be I think, even if the lockbox holds some dark shit.