If you meant a specific (e.g., LFS v1.0.5 for D2R 2.6), please provide the exact mod version and D2R build number, and I can give more precise file-based instructions (still within legal limits).
Download the LFS Mod Offline Fix and extract the contents.
If you are using a mod that comes in a folder (e.g., a loot filter), you don't need to overwrite game files.