Changing item interaction?

[Damascus]

I've done some searching, but haven't quite been able to figure out how to change the way a player interacts with an item. I know that I have to make new files for each version of the item, but I don't know what to change about it.

Example 1: I've laid the arm of a corpse on the ground, but want the player to be unable to pick it up and move it.

Example 2: This one's more complicated. I want the player to pick up an item into their inventory (a stone), but when they use it on a stand, you can't move it but can use an item on it. Then, once you do use the necessary item on it, it becomes an item that you can now carry and throw like the normal stones in the game.

I realize that last example will require three different item files, but I don't know what I have to change about them to make them interact differently.