Board Thread:LotR Mod Technical Support/@comment-29253515-20200115163047/@comment-27219153-20200116055933

You can remove all those dimensions and your world will be fine. Although, if you probably shouldn't remove any dimensions you've built in, unless you want to lose those builds.

As for "copying builds between saves," each save has a level.dat file which has a list of all the blocks and items and what their ids are. Since your other saves have a different level.dat, the ids won't match up. You can use the Minecraft Region Scanner to convert builds to the right ids before you move them over.