It is a good idea to create sub-levels. Have one with lighting A and another one with lighting B and then make the one visible that you need.
Your lighting actors might just be in another level.
- Load the other level as a sublevel
- select the actors you need in this level
- right click on the level you want the missing actors to be
- from the context menu choose ‘move selected actors to this level’
You can also copy/cut/paste between levels
It is not good to copy a level in Windows explorer. Better select all actors in unreal and copy them into a new level. If you copy the level in win explorer you might get 2 levels with the same name in unreal’s browser.