Does I must re-flash the os system image and the DTB? If I change the device tree,

I use the jetson TX1 ,R28.2.
Does I must re-flash the os system image and the DTB? If I change the device tree.

You can flash just the device tree. The flash.sh command line “-r” option says “reuse” the system.img…this is part of the configuration…the other half is to name the target as the device tree (the "-d " option).

Example:

sudo ./flash.sh -r -d <path/to/device tree> mmcblk0p1 jetson-tx1

Do beware that in a booting system some parts of device tree are in different locations. If you are looking to change the device tree for the Linux kernel this is probably what you want. There may be other places too for earlier parts of boot…try the above first.