if you have to redo windows and reinstall inventor or upgrade to a newer version of inventor you loose all the content center parts you imported. in some cases you want to transfer your custom library to a colleague. This is my solution to the problem don't know of any other way.
First step is to go to control panel and switch on "Show hidden files, folders, and drives"
Go to the file path shown in the attached image.
Search for the file with your library name and copy it. when done redoing your windows and installing inventor copy this file back into the folder. Do not delete any files in this folder.
If you installed a new version of inventor go two folders back and select the folder with the newer version name. as shown in the attached image.