Not true with all routers. If I modify a setting, there is no need to save. Unless I am in safe mode, the change is immediate and permanent. Good thing I have a serial port to access the router to get the default config back.
This is probably the case if you use the Web interface for configuring things. But if you use the command line I haven't seen a device yet that automatically saves that in a non-volatile storage.
Yeah I've changed other things on this router and changes like this are usually persistent. For example I've changed the brightness of the LEDs by simply piping numbers into the right /dev and it stays that brightness after a reboot.
I didn't write you should reboot the device but unplug from power. That way there's no possibility to shutdown the device and store current settings in EEPROM or flash.
for example br0 is mentioned in various scripts on the device - so what happens when the web interface tries to configure stuff using these scripts that reference br0? If the bridge is split, that means there'll be two separate devices to configure but again the web interface only expects one.
After doing such stuff on the command line you shouldn't use the web interface to configure the device. I just wanted to give you an opportunity to use your current device and have the segments separated.
I don't see a chance to change anything on the Arduino side. Embedded devices usually don't have enough memory to cache an ARP table.