Many (if not most) trading systems have an expiration date.

By the time you have acquired your hard-earned $200, how much time has passed? 1 week? month? year? You will need to re-evaluate and fine-tune your system. Then, and only then, can you consider re-adjusting your capital after making a profit.

By the way, if you turn off the system after gaining 200, and then turn it on with the capital set at 1200, you are deliberately disobeying the rule!