[SCRIPT] Lever pushing a bookshelf that has books in it

[Khyrpa]

From what I remember, you can only have one model in the ModelEditor at a time

Yep, seems like so.

You can open up a .ent file with notepad and look inside, its mostly just the variables for how that entity behaves and where the .dae etc. are located.
If you are hardcore, you could write .ent file from scratch without model editor.

You could also try to create a new entity out of the bookrows that has physics, but no interaction.