Any information on how to disable the RED LED on AR300M (I know this shows it has booted but I’d rather switch it to the middle LED.
No, you cannot. It is power and hardcored.
I used a simple black tape… 
I have my own image built with LEDE and it can be controlled. Not tried in the factory image.
Luci:
system/led
add LED Name: gl-ar300m:system
trigger: none
This switches it off.
You can configure it for whatever you like. I loaded kmod-ledtrig-heartbeat and have it flashing to indicate a successful boot. You could also set it to indicate wan,lan or wireless data or even a USB active.
Sorry. Actually I answered that from memory. It is the right hand green that defaults to always on (viewed with the ethernet ports towards you).
Assuming we are actually talking about the AR300M…
The red is WiFi.
The leds seem to be named as follows:
gl-ar300m:system (green)
gl-ar300m:lan (green)
gl-ar300m:wlan (red)
and can be configured in Luci
@alzhao On my device (AR300M) green is hardcoded for power, has this changed on newly produced models?
I think your original post is confusing everyone
The red led is the left most when holding the unit with the ethernet ports towards you and seems to be configured as the WiFi led by default in a mode to be on with NO traffic and flashing OFF with traffic. My reply above shows how you can control all three using Luci UI, at least in the latest LEDE firmware. If included in the GL firmware it will be under Advanced options.
@wifird, actually all LEDs are configurable. We hardcored in some models but we found that it is not the best solution. So we will use configurable LEDs. But the power LED will still be always on by software control. You will be able to turn off or configure manually.
Great @alzhao!
And apologies @bluewavenet for being confusing, got there eventually lol, thanks for the help 