The problem is that cold is merely the absence of heat, you can't inject cold into something or generate cold, because there is no such thing as cold. It's kind of like how we can make a light bulb, but we can't make a dark bulb.
Sadly, a mini black hole would suck up everything around it. Much like a tiny Katamari Damacy, it would quite quickly consume everyone and everything around it. Of course after not too long it would become a regular sized black hole.
Some mini black holes do not grow into black holes. They collapse. The issue is that they aren't stable for any decent length of time. Fractions of a nanosecond.