I began playing my ruby version again, when I started wondering about all kinds of different things, such as, is it possible to get behind the daycare center without a game shark or duplicate items? This is what I'm afterifyou know of anything like these feel free to post them here

There are no in-game cheats for any of the pokemon. There are glitches, though. There's a nice list of all or most of them and good descriptions for each that can be found on bulbapedia here: List of Glitches in Generation III