This is a question I posed on 'Hypothetically, this is madness!'. I thought that everyone should be able to answer it, not just one person.
Q: What would you do in this scenario that I have been thinking about all day: You suddenly discover that you are able to make a nuclear explosion from a single atom, confine the energy, and convert it into matter of any kind you want?
(I personally would build tons of stuff, and then make legions of lonsdaleite* soldiers with a hive mind controlled by me. I would enter the UN and demand that I get to make my own country out of a region that is not currently classified as a country, such as the Western Sahara. My threat would be that these lonsdaleite soldiers would take the area anyway. If any didn't agree, I would give them an example of just how tough they are, IE make one use a machine gun on one, and because it is lonsdaleite, it will be unaffected. Then I will establish the country, and make it into my dream utopia world using shaped matter. After a while I'd get bored and set off to do stuff such as end world hunger with shaped matter, and other fun things, until the world has no threats to it at all, due to the matter having solved problems.) Being an N is so fun for fantasizing.
*Lonsdaleite is a material estimated to be 58% harder than diamond. With proper application of very high indentation loads, it can become 78% harder than diamond.