There’s some misunderstandings going on here.
1-WMR works with 4.17
2-WMR does NOT work with 4.18
3-There is a pull request that reverts SteamVR back to the way it was in 4.17 for 4.18 but you have to build 4.18 from source and then apply the pull request at https://github.com/EpicGames/UnrealEngine/pull/4356
The github repos are all there as usual at https://github.com/EpicGames/UnrealEngine. You can fork and branch it to create your own changes and pull request if needed.