I couldn't find any template projects for NX payloads, so I made one based on Lockpick_RCM, with the help of its developer, shchmue.
Inject the .bin file over USB with TegraRcmGUI or a similar injector.
Install devkitARM and run make.
= Massive Thanks to CTCaer! Lockpick_RCM is heavily based on Hekate. Beyond that, CTCaer was exceptionally helpful in its development.
This project is under the GPLv2 license. The Save processing module is adapted from hactool code under ISC.