is it possible to make an ore from the ore dictionary drop a custom item? for example, lead occasionally dropping lead-210.

Given that I never wrote anything with the ore dictionary, the first way that comes to my mind would be to register an EntityJoinWorldEvent handler, that checks whenever an EntityItem is spawned. Then, if it contains something that is registered in the OreDictionary as oreLead, it replaces the ItemStack with what you need, or spawn a new EntityItem with the occasional sub-drop, or whatever you want, even creating a nuclear blast or a host of creeper if you feel like so.

It was completely off the top of my head, so its not guaranteed to work.

Indeed, haven't thought about that. It may be twisted to work anyway, but that may require a lot of extra infrastructure.

does anyone know what the ore dictionary name for lead is?

 

EDIT: also does anyone know how I'd call the event handler? and would this work for checking if it's lead or not

if(OreDictionary.getOreName(enti.func_92014_d().itemID) == "LEAD ORE DICTIONARY NAME")