I would think if your spooks had the ability to change the inside of a diamond to something else they would be able to change the entire diamond to something else or at least be able to levitate the diamond.
Your spooks suck. They don't even aspire to doing something measurable for the million dollars. Your spooks will rightfully stay in spook oblivion unless you come up with a measurable way the spooks can be verified.
There is absolutely no need for this.