How do you make or mod item spawners?

[justalyxx]

I've seen a few mod releases for item spawners, but none for books. How do you make such mods i read that it was kind of simple? or at least possible. My main attraction here is to make books respawn or to have 3 of each spawn so you can maximize durability on anything you want (potentially, not sure if they actually would stack). guess the game is kind of old now but thought i'd ask