Only above DTB will be used.
I don’t know why you need to overwrite it.
Please just copy it → modify it → replace it as following:
$ cd ~/
$ cp /boot/dtb/kernel_tegra234-p3701-0008-p3737-0000.dtb .
$ dtc -I dtb -O dts -o devicetree.dts kernel_tegra234-p3701-0008-p3737-0000.dtb
(modify devicetree.dts as you want)
$ dtc -I dts -O dtb -o kernel_tegra234-p3701-0008-p3737-0000.dtb devicetree.dts
$ sudo cp kernel_tegra234-p3701-0008-p3737-0000.dtb /boot/dtb/kernel_tegra234-p3701-0008-p3737-0000.dtb
You can run the following command on your board to check the current configuration through extracted_proc.dts
$ sudo dtc -I fs -O dts -o extracted_proc.dts /proc/device-tree