Once you’re ready to save a custom MIDI mapping, click Save to User Mapping in the drop-down menu located in the top right. Then, click Save User Mapping to File… and save the .nka file to an easily recallable location on your hard drive. 

To import the custom user mapping, click Load User Mapping from File… from the drop-down menu located in the top right, locate the user mapping file (.nka) on your hard drive, and click Open

If you would prefer the custom user mapping to “stick” as a default to the library, save the mapping by clicking Save to User Mapping in the drop-down menu located in the top right, and either re-save the .nki, or create a snapshot.