I don't know about Tim, but the question still seems to vague to me.
When you say 'add a new tool to the existing library', 2 possibilities come immediately to mind:
1) you are using CAM and want to describe a physical cutting tool and add it to the library
or
2) you want to make a 'user defined feature' and add it to the library that you already have.
Unfortunately, I won't be of much help if either one of these is the case, but maybe it will help clear up the question for someone who can help.