Hope this helps

Things your gonna need:
At least a 1gb usb
modio
Black ops gpd editor
Xero

On Your Xbox:
-Insert your USB and go to memory and click on your usb device.
-Format your usb (This will delete anything and everything on the usb so make sure there isnt anything important on it)
-Then go to your main HDD that has the profile that you would like to mod the classes and move it onto the usb.
-After that remove your usb and insert it into your computer.

On your computer:
-Ounce youve inserted your usb open up modio(Download Link Above)
-Then in modio click on explore device and click file and open device.
-Keep clicking until your find the file that says somthin close to E000000000 or sumthin that starts with an E and has a bunch of numbers behind that.
-Right click on that file and click extract, extract it to the desktop.
-Minimize that and then drag and drop the file you just extracted(which is your profile) back into modio.
-Then on your profile tab click on the contents tab.
-Scroll down until you find a file that says 41560855.gpd
-Right click that file and extract it to your desktop.
-Next open up Xero(Download link is above)
-Click Black ops gpd editor.
-Then click open and click open .gpd
-Open up your .gd file that you extracted.
-You should see three sections and a bunch of text in each section dont touch any of the text.
-Go to the far right section and scroll to the bottom of it youll see where it says "Custom Class 1" and soo on.
-Delete the Custom Class1 part and type in watever youd like(15 Characters max+That inculdes the color codes.)
-Example: "^1Slade!"
-The ^1 is the color code which is red ill put a list of all the color codes.
-Ounce youve finished editing your classes click the save button you should get a notification saying that it saved succesfully.
-Then go back into modio and go back to your profile contents
-Right click the gpd file that you first extracted and click replace file.
-Find the .gpd file that you modded and replace your old .gpd file with it.
-Then go back to the main profile thing that shows your profile and device I.D's
-Click Rehash and Resign
-Next close out your profile and open up your Device explorer that you had open.
-It should still be at your profile or the E000000000 thing.
-Right click inside that box and click insert file
-Insert your profile that you editied back into the device if you did everything right a little notification should come up asking youd like to overwrite your old file click Yes.
-After that close your device up in modio and take out your usb and put it back into your Xbox.

Custom Class Colors:
^0 = Black
^1 = Red/Orange
^2 = Lime Green
^3 = Yellow
^4 = Navy Blue
^5 = Light Blue
^6 = Purple
^7 = White/Default
^8 = Black

On Your Xbox:
-Go to memory and click on usb:Gamer profiles then click on your profile and move it back to the HDD
-Sign into your account and start up Black ops.
-Go to xbox live and go to your classes if everything was done correctly you should be greeted to the sight of some beautiful modded classes.

This took ages haha hope it helps