Use Amlogic USB Burning Tool to "Read" from your device before writing. Without this, you cannot revert to stock if something goes wrong.
However, if you have ever used a stock S905X3 box, you know the ugly truth. The firmware is often riddled with bloatware, spyware, backend telemetry, broken HDMI-CEC, and a disastrously slow launcher. s905x3 custom rom
Install the WorldCup_Device drivers and Amlogic USB Burning Tool v2.2.4 or higher. Use Amlogic USB Burning Tool to "Read" from