[matt5250]

your natural rating is not changed at all, you just have a modifier increasing your stats when it's used in crimes and combat. so if you have 19 acc and 1980 dev points, you wil still have 19 acc and 1980 dev points after the acc upgrade but in battle you will be considered to have a 20 acc, then when you get another 20 dev points you will have 20 acc but will be considered to have a 21 acc for all intents and purposes.