To get this to work through Cydia instead of replacing the original.
First you have to make a new theme in Winterboard (posted throughout MMI). In your "Theme" folder you need to make a new folder titled "Folders". Then once in your "Folders" Folder you need to make another folder and title it which ever carrier you use. For me, I am a legit ATT customer so my new folder name is "ATT_US.bundle." Then put your "Default_CARRIER_<"your carrier">.png and the "FSO_CARRIER_<"your carrier">.png into the folder, restart and you have a new carrier logo.
So for me it is <Private/ Var/ Stash/ Themes.59qine4/ Compton's Theme/ Folders/ ATT_US.bundle/ Default_CARRIER_ATT.png and FSO_CARRIER_ATT.png
If not ATT user you can get the Folder name by SSHing into phone under. System/ Library/ Carrier bundles. They are at the bottom. Then just plug them in above.