Yeah, play with your profits will be safe for you to keep your capital safe. If you lose you will just lose your profits not your main assets.
How you got your profit? After risking your hard earned money you earned some profit that means that profit also your money. So whether you play with profit money or your money both are same as per me. As long as you set some limits for gambling funds should be fine. Once I get some profit I will withdraw and invest that money in some other place and again I play with my fixed amount next time.
Having a plan and setting up limits for yourself is indeed the best option and you can manage your gambling life based on these simple rules and be successful because you will only loose certain specific amounts of money and you cannot exceed the limits which you've set for yourself.