There are segments in the game where you have to protect Ashley (The President's Daughter). Have you gotten to those points in the game and if yes, does the Trainer Health option work for her as well?
Actually, the rating is only connected to the score, nothing else. Search with cheatengine and set to 100000. The address is always the same for all characters on all stages. Just wait for the go, set the zero to 100000 again and survive the 2 minutes. After 45 minutes, the 'handcannon' is yours.
Same, are you EU region? I have a feeling that might be the issue since the same thing happened to my Sleeping Dogs when I bought it in Germany and apparently got the low violence version. I would hear activated but nothing would happen.
Perhaps if the devs aren't too busy maybe just a looksee? I crash as soon as I hit the infinite ammo and reload after firing. Actually none of the options seem to work but I hear activated.