renaming a app name in menubar

[nebulOSX]

Hello,

Just to set the picture, me and my friend want to edit Mail.app to Post.app (we're british ) purely for fun. a bit of a novelty and to be different lol. I have navigated into the mail package and edited the main .Nib with interface builder, but no matter how much i change the main menu app name nothing happens, it just stays as "Mail" .

i have also looked in the plist file inside the package and the rest of the .Nib files in the resource folder and nothing. so basically i want to know how to change an app name in the menubar, just interested to know if anyone knows howto, thanks a lot

(p.s, i hope this is in the right forum section :s)