The through cars to LAX, one Sleeper and one Coach will be transferred as usual. The core Eagle consist will remain unchanged between the Sunset days and the non-Sunset days. On Sunset days the Sunset conveyed Sleeper and Coach will simply be tacked on to the Eagle, so on those days the Eagle will have two additional cars than they do now. So there is no issue of accommodating the LAX through passengers in the cars of the Sunset that comes from/goes to New Orleans
On the non Sunset days there will be no car switching to do at SAS. At present apparently two cars are taken off and kept there. Originally they were kept as protect cars and were a phenomenally poor equipment utilization.
Additionally there will be a St. Louis drop Coach.
Here is the Trains article that explains it, for those that can access it. It may be behind a pay wall for some. The relevant text is quoted below the link.
https://www.trains.com/trn/news-rev...dedicated-sunset-through-cars-special-report/