Someone isn't quite feeling like themselves today. In fact, they feel very distinctly like someone else...

Maybe HG Wells leaned too hard on the Soul Tracer and accidentally swapped Lois and Clark. Maybe Mxysptlk thought it would be funny to turn Lex Luthor into Jimmy Olsen for a day. Maybe Perry White is the latest host body for the Quantum Leap project. However it happened, what does this person do in their new skin?

This sounds like a certain fourth season episode -- Only, I am sure that any fanfic writer here could come up with something better than the official version...

Actually I can see Jimmy loving a chance to be Lex Luthor for a day.

Hmmm, good title for a short story...

There is a story on Twisting the Hellmouth where the halloween costume spell swaps Lex and Xander. It is wonderfully twisted in places as Xander decides to change things. https://www.tthfanfic.org/Story-32334/dogbertcarroll+Lex+Marks+the+Spot.htm