Is there a way to change Poser 5's default libraries when entering and exiting rooms? For instance, entering the Material Room defaults to the Material Library. Exiting goes to the pose Library. Changing libraries, while in a room, will stay with that library when exiting the room. It would be nice to change the defaults to what I want to do.

I don't think so. The info about which folder you used last is stored in Runtime/prefs/libraryprefs.xml Each time you change the folder you're using, this file gets updated. Personally, I always take care, before leaving a room, to go back to a root folder, so that next time I enter the room Poser won't spend 30 seconds building up all the thumbnails again. If you feel brave, you might try to set the folder you wish Poser to default to for each category, close poser, and then set the libraryprefs file's properties to "read only" in order to avoid any further change. Please tell us if it works... but I assume no liability if it breaks up something !