This method makes sense if you are working on your own computer, where you can update your own libraries and use them again.
Look under C:Program FilesLTCLTspiceIV
(or C:Program FilesLTCSwCADIII )
Go to the directory libcmp
Look at the list of standard devices to figure out which kind you want, such as:
standard.bjt
standard.dio
standard.jft
...etc...
Each line in each of these files has a model for one device.
Add a line with the .model line for your device to the end of the appropriate file using a text editor.
Note you may have to adapt the model line to match the pattern in the file. It should be pretty easy to figure out.
Now when you open LTSpice, you should be able to pick the device you've added as though it was one of the existing models.