Can Android and/or Apps handle switching an SD card temporarily? I have a lot of apps and app data on my SD card. I know Android handles unmounting and remounting that card very well.

However, what if I temporarily insert another SD card onto my Android device - will the system handle this OK and be back in the same state when I reinsert my original card? What about apps, should they in most cases handle this well too?

What I'm worried about is that Android seeing the empty SD card decides that I've removed all the apps that I had on my SD card, and any apps I have left will also think I've removed their data and rewrite some internal indexes accordingly...
AFAIK it is very difficult for an App to identify the inserted SD-Card. A regular App should be able to handle the case if the SD-card is not available (ejected or connected as drive to the PC via USB) but I assume that most Apps can not handle the case when you regularly switch between two SD-Cards.

In general you should not start any Apps that use the SD-Card while you have inserted the "wrong SD-Card".

Regarding the Apps moved onto SD-Card - this is a different topic. As my device does not allow to switch the SD-Card while running I have no clue what happens e.g. to the app data in your device if you switch the SD-Card.