First, browse to:

C:\Program Files (x86)\Steam\SteamApps\common\Counter-Strike Global Offensive\csgo\scripts\items

then open the File called: items_game.txt. (u might want to copy a backup of this File)
As u open the File in ur Text-editor, hit Ctrl+F to serch for "C4".
Edit the Value of "item_slot" to "melee" instead of "c4".

Save and close the File, start ur Game and browse the C4 in ur Inventory.
Buy a Nametag and then rename ur Bomb in whatever u like.
Now u should be able to use the C4 just as a regular Skin.

After u renamed ur Bomb, u should go back to items_game.txt and
change the Value of "item_slot" back to "c4".