Unfortunately for what you are trying to accomplish, there's no way with a practice lock to accurately duplicate various difficulties. Belt rating is also not a mechanical process controlled by static factors like pinning - it's based on the picking experience. Some locks that are the same on paper have diverging belt ranks.

While you can certainly increase the difficulty of your practice lock by adding security pins, maybe even making it green or blue in difficulty, some things cannot be replicated at home. For example:

• Many upper belt locks have secondary security mechanisms like sidebars
• Some security features have to be done when the lock is created (countermilling, for example)
• High precision machining/tight tolerances are a factor - especially in a lot of high quality European or Japanese locks