I've done LOD for many worlds, thanks Mr. Velicky, how is it done/can it be done for interior cells?

It can't be done for interior cells. Any place that would be large enough to require LOD would have to be set up as a worldspace. Bethesda did this for certain "interiors" such as Blackreach.

I believe it can be done if the cell is set as an exterior cell, not interior. Could be way off but sure I've read that before.