Thats perfectly acceptable. If you want a pokemons stats to be different, youre welcome to do so. Rules in rpgs are just guidelines after all. I suggest you give it a dry run with a combat scene and look at the character sheets and such before deciding on changes. You might change your mind once you have a better handle on the rules. And as far as I know, that rule has been removed. Or if it is there I think its stupid and ignore it. The status effects lower defense and special defense to be more realiatic. If you're burned or poisoned, everything's going to hurt lot more. It helps even out how slow poison and burn effects lower health. Ive never had a player complain, even when they fought against a poison master.