Whenever the LotR mod updates, all kinds of cool new content is added. But, if you have already generated a lot of chunks, you will not get to experience some of this new content in your old terrain. The simplest way to deal with this is to simply explore more terrain; generally, only a small percentage of the potential chunks in a world will ever have been generated. But if you generated a lot of chunks and you wish to have those regenerated while keeping your builds safe, there is a way.