re-assign the @ button on keyboard?

[NewYorkLaw]

I like the concept of the keyboard @ button, which when you hold it displays three choices, @gmail.com, @yahoo.com, and @hotmail.com.

HOWEVER, I don't use any of those. Where is the file that I would alter to change the choices to what I do actually use? My phone is rooted, so it should not be a big deal, but I cannot find it.

Thanks,
Pete