How do I edit the starter pokemon and gift pokemon in black and white?

[celloplayer190]

Hello, I am currently working on a rom hack for pokemon black. One of the things I need to do is change the starter pokemon. I have searched this site and the internet for tools or hex editing tutorials to do this, to no avail. I do not care if it still says "snivy," "tepig," and "oshawott" in the selection screen. What I want to happen is if you pick the grass choice, you get chikorita, fire gives you cyndaquil, and water gives you totodile. Additionally, I want to make it so the dreamyard monkeys get replaced by the gen 1 starter of their respective types. Could anyone give me a rundown on how to do this?