What I do is create a new component for the application.
Assuming that if the part is in the schematic, it must have connections some where to the PCB.
Create a new DEVICE using the desired SYMBOL and a new PACKAGE with just the connections you are going to use on the board.
If you have PINS in the SYMBOL that you don't want to show up on the board, the Library editor won't let you finish the DEVICE without connected pins. In that case, just make a copy of the SYMBOL with a different name, and replace the unwanted pins with essentially a drawing of the pins on the SYMBOLS layer. Now when you create the DEVICE, it won't complain about the "unconnected pins".
I do that with things like transformers that the primary connections are in the chassis, not on the board.
I also have many DEVICES in my personal library that have no pins (great for including package drawings for your schematic). If you just create a SYMBOL that doesn't have any PINS, the editor will not demand a PACKAGE when you make the SYMBOL into a DEVICE.
I hope that is what you wanted to know
Another hint:
Create and (or just) open a library and leave it open, then go to the "control panel" and browse the existing libraries. You can then just right click on a DEVICE or a PACKAGE, then select "Copy to Library", the item will be copied to the OPEN library. I collect all my most-used stuff to a "personal" library. Now you can edit them to your heart's content. The only problem is that you can't import just the SYMBOL without it's packages. Delete the new DEVICE (not the SYMBOL) or the editor won't let you modify the SYMBOL while it is "in use".