Using 'Setting-Breaking' OSR Adventures

  "It's a great adventure/module/hexcrawl, but it wouldn't fit into/it would break my setting!"
  I've read that countless times. I perfectly understand it too. Maybe it's because the adventure can change the world in a way you don't want to have to keep dealing with afterwards. Maybe it's because the adventure assumes something that you just can't casually plug into your campaign, like an adventure that assumes some sci-fi elements are constantly present but you've been running a purely medieval fantasy game so far.
  Well, why not use it anyway... On another world? Could be another dimension or another planet... Yes, another world with Elves, Dwarves and Hobbits too. And yes their languages are the same. Let's not over-think it. (Or in fact do over-think it and come up with a cool in-story reason for that!) You can break that world all you want!
  I'm not saying there couldn't be long-term consequences anyway... If the PCs accidentally broke a whole planet, their own gods might be wary of them when they go back home. Or survivors from that destroyed world might go after the PCs looking for revenge. Of course I'm using the most extreme of examples where a setting is broken beyond repair, but it's just to mean that adding new dimensions/planets opens up possibilities and allows you to use those adventures.
  As for how you'd approach such a thing, there's already a lot of material for that out there. 2nd Edition AD&D had 'Spelljammer' and 'Planescape' that offered different ways to travel between settings. Personally I would simply grab the 'Spatial Travel' spell from Realms of Crawling Chaos. Good old dimensional gates inside a dungeon can also be an effective way to get your players elsewhere.

  There's also the controversial Ravenloft Mists, which are a railroading tool for sure. For the uninitiated, magical mists randomly grab you and send you to a realm of horror, in which you're trapped for the duration of the adventure or until the GM feels like bringing you back home.

  I'm not saying I'd never use them. In fact, despite its railroading element, it can be fun to suddenly take players out of their comfort zone every once in a while. But I'd certainly try to find a reason for the mists and I'd even offer a chance for players to avoid them entirely. For example, I'd tell them they see unnatural mists moving near their encampment. If they decide to pick up their stuff and get the heck outta dodge, that would be it; No Ravenloft adventure. If on the other hand they 'decide to investigate', then they'd end up in Ravenloft.

  But I digress. My point is... That adventure you really wanted to use but it wouldn't fit your campaign's setting? Just use it in another world and you're good to go!