Is it possible to have multiple backgrounds for a room and change them at will?
For example a day and night version of the same scene?
Yes. You can have up to 5 backgrounds for each room (0-4, 0 being the default background frame). You can use them for animation purposes or what you mentioned above, night and day scenes.
You can call it using:
SetBackgroundFrame(int frame);
You can also of course use variables to check when they should be changed at room load.
merci
You can also use the Ags_theoraplayer plugin by Scothc to have a video as a background
And you can use the DrawingSurface functions (formerly the RawDraw functions) to make dynamic modifications to the room's background.
And you can use characters/objects in the room for animations of specific areas.
So yeah, there's lots of ways to do this. The easiest way for a nighttime background is as Snake advised you. ;)
You can also fade it in and out so you can create a day night cycle of some sort.