Altering Evolutions

Hey there. I'm currently trying to change every evolution, removing both happiness and trade evolutions for simplicity. I've done most pokemon however I want to keep the Karrablast/Shelmet evolution where they need each other in the party in order to have an evolution (similar to Pancham needing a dark type, but a specific pokemon). I've tried a lot of different things, but can't find how to do it. Could anyone offer support? Cheers.