I've been working on levels for Uru Live if it ever happens again. I have a mommy note from Mr. Fryman at Cyan legal but can't post anything public until his OK.

To your first question, you can't save an animated X format model specifically. The obj file is saved with modifiers. Things like object type: door1, speed: 15, collision: 2, etc is saved with the object and only make sense to the game engine. These may be included in the obj header or packaged into a file the game reads. If FPSCreator packages modifiers with the object then you probably have an option to make user object menus where you can use the same door over without setting modifiers again. These files probably can only be saved into FPSCreator unless you want to use blender and a hex editor and write your own decompiler with python scripts.

The door seems to be an animation on a flat plane. The object doesn't move, the animation does. while the door is "open" the object has no collision so your character passes through. The animation for his red accordion door is 30 frames; 15 to open, 15 to close. You could make your own animation in bryce then convert it to TGA and use it. If it took 40 seconds to open and close then you would set the speed to 20 so the door stopped in the middle of the animation when it is opened.