Roseanne – Lecy Goranson then Sarah Chalke then Lecy Goranson then Sarah Chalke again
This is probably the most complicated switcheroo in the history of tv. Goranson originated the role and played Becky for 5 years, then Chalke took over when Lecy went to college.
Lecy was then able to work her college schedule so she could work on the show again, so she and Chalke alternated the role. Finally, Lecy just wanted a normal life so she left for good in the last season and Chalke carried the role home.
As for the upcoming revival, it looks like the original Becky is coming back, with Chalke in a different role that’ll poke fun at the change.