You could try to use dd to update specific partition. But please note that dtb needs to be “signed”.
During the flash, the flash script will sign the dtb and flash that signed dtb to tegra. If there is no sign, the boot procedure will reject this dtb.
However, you may still need a host pc to do this work.
For the purposes of signing without flashing take a look at the flash.sh script argument “–no-flash”, and if you are looking at using tegraflash.py directly, take a look at the argument “–keep”. Keep in mind that you can edit flash.sh, and that flash.sh calls tegraflash.py.