He's right; this wouldn't be hard to do provided you have other scripts that can help and whatnot. There are a lot of Cheats scripts throughout
RMXP.org and Creation Asylum if I recall correctly, but I don't think they do what you want in particular (That is, button combination at the title screen).
If you want one of those exact combinations, like typing 'hidden test' in the Microsoft XP Pinball game (For example), you would need some script that maps the whole keyboard...Erm, Cybersam made one I think? That's in .ORG too...I can't provide anything, but I can do a little hint here and there I guess. Sorry.
If the combination is pressed, a global switch/switch is turned on which allows the Cheat Menu to show~ Whee, obvious idea.