Swapping rear dearilleur

Dax Ford said:

Looks like I forgot to get a tool in order to do this- Cable cutters with a crimper on it. Is this what I need to swap rear derailleurs?

I couldn't pull my old one off becasue the cable wouldn't pass the adjusting barrel on the old derailleur.

I guess I need to cut off that little bit of extra cable and crimp on a new end fitting to the cable after I install the new derailleur right?

Is there any way of sparing the cable from being cut in order to remove the derailleur?

You should have enough slack to reuse the cable after you cut off the crimp. Also, you may be able to unscrew the barrel adjuster from the old and use it on the new der thus not having to cut the cable.