If you are trying to change system files I'm assuming you are rooted...
I've heard that Android UOT kitchen can do this though I've never used it myself but there is a forum for modding roms on this site. http://forum.xda-developers.com/forumdisplay.php?f=613
I myself have used an app called ROM Toolbox pro( I forget the price ). It allows you to change many things like signal color and style, battery style, etc. It's selection of mods differs from rom to rom, as does it's effectiveness but for me it works most of the time(on an Inspire with many different roms and a Flipside with cm7). It also comes with many other great tools. If your quick enough you can try to apply a mod, restart your device, and if it doesn't work get a refund.(I think its a fifteen min window) Of coarse make a nandroid