How I know which name to give them in order for them to be included in the new built DT?
As far as I understand, for each .dtsi file there is a .dts file which includes it.
So I have to “discover” the suitable .dts file that is being used when building the general DT, look for the .dtsi name that it includes for the pinmux settings (for example) and than change my new pinmux.dtsi for that name.
Can you explain the full process for taking these new .dtsi files, create a dt overlay and load them after reboot without re flashing the target?
After you get this 3 dtsi, pleas just refer to the following note to place them to the correct directory on your host PC. Copy the padvoltage.dtsi and pinmux.dtsi files to the <Linux_for_Tegra>/bootloader/t186ref/BCT/ directory and copy the gpio.dtsi file to the <Linux_for_Tegra>/bootloader/ directory.
pinmux.dtsi should include gpio.dtsi, please just confirm if the file name is correct.
Then, you should configure the board config(For Orin NX, it is jetson-orin-nano-devkit.conf) as following for your new generated dtsi.