@GamingProX66
https://github.com/Laupetin/OpenAssetTools
This is the mod tools you can use for black ops 2. Its still very limited as its still being massively worked on, but its semi easy to use and you can find documentation on the web as well as the github of the project for information and how it works. "Custom maps" are possible if you consider maps like the Simpsons and Minecraft map from the forums "Custom" but its still got a looooong way to go as far as "Custom" goes. Developments have been added recently that allow this to be expanded but if your looking for something similar to radiant, nothing like it exist publicly atm