My question is; What would I need to do to change the usb cord for my deck numberpad.

I've got the small deck keypad and seperate deck numberpad.

The LED usb cord for the numberpad is not modular and is hard connected inside of the numberpad. This has been very annoying, since I don't want usb led and I assumed the numberpad would have an interchangeable usb as the keypad does.

My motherboard always feeds power to whatever is plugged into it whether it is turned on or not. Since I can't turn the usb led off, I have to constantly un-plug and re-plug the deck numberpad into the computer. How annoying

There's really no way to do that. Sorry. However, there are settings within your computer that you can change so that it will power down when you turn your computer off.
....Deck Girl Amy

I kind of expected that, but I hoped someone would say something like, "cut the usb cable where you want to strip the cabling, then cut another usb ... twist the green wire around the red one ... etc." I guess I'll look somewhere else on the net for that.

kind of like this...
http://www.computerstuffs.co.uk/pcmodding/electronics/mobo_usb.html
http://forums.bit-tech.net/showthread.php?t=89344&highlight=cut+the+usb

don't worry. I'll do a few practice runs before doing the real thing!

Well if you wanted todo this I'd suggest unsoldering the cable and attaching another in the same way the current one is.

If you want to connect the wires then DO NOT connect red to green that'll fry your keypad!

It would be
[+5 Vdc] -> [+5 Vdc]
[Data+] -> [Data+]
[Data-] -> [Data-]
[Ground] -> [Ground]*
[Shielding braid] -> [Shielding braid]*

*note the dark blue from above will be black wires (shileding will be silver/copper/the wire wrapped around the outside if the other wires)
I had to do this when the BG color is black

I did it.