Drop That is a mod that lets you set the loot table for any mob or object, by specifying the index of the item you want changed. You can either add or replace the existing drops. You can add as many drops as you want, and their drop chance or drop range can be customized as well.

It can either be a client or a server. The server version is more complicated, because it has to handle the configuration of the clients. However, with the client version, you can run the game with just one configuration file, which is enough for most people.