ACID means more than atomic updates, though. To be ACID-compliant, you'd have to be able to group several changes to the registry and have them take effect either all at once or not at all.
In cases when I need to write several values atomically (e.g. in a program with persistent window positions, after user moved a window I want to write all 4 coordinates of the rectangle), I just keep them in a single value, either string or binary. Even without KTM, registry API already guarantees value writes are atomic.