This is from my bookmarked tags, https://sites.google.com/site/pk2devicefileeditor/
you must select a device similar to the device you need to add
The program is generally only useful for adding new parts not currently supported by the devicefile bundled with the PICKit 2. The process, after opening the devicefile, is simply to choose an existing PIC from the list of devices, right click on it and select Duplicate Item. There will now be a copy of the part you selected. Change the properties of the new part, including the part name, to appropriate values for the new part. Then save the file and you're done.
It's possible to find the appropriate fields from the datasheet and programming specification documents for the particular PIC part. Sometimes it's a little bit hard to find what you're looking for, or to even know what you should be looking for; feel free to ask on the Microchip Forums (in particular under this thread: PK2 Device File Editor Thread); there's some very knowledgeable and experienced members there.