To Disable Onboard LEDs:

led1 - Is Power LED "RED"
led0 - Is Active LED "GREEN"

echo 0 | sudo tee /sys/class/leds/led0/brightness > /dev/null
echo 0 | sudo tee /sys/class/leds/led1/brightness > /dev/null

echo 1 | sudo tee /sys/class/leds/led0/brightness > /dev/null
echo 1 | sudo tee /sys/class/leds/led1/brightness > /dev/null

To Start On Boot:

sudo nano /etc/systemd/system/disable-led.service

And Copy/Paste The Following:
And Save

[Unit]
Description=Disables the power-LED and active-LED

[Service]
Type=oneshot
RemainAfterExit=yes
ExecStart=sh -c "echo 0 | sudo tee /sys/class/leds/led1/brightness > /dev/null && echo 0 | sudo tee /sys/class/leds/led0/brightness"
ExecStop=sh -c "echo 1 | sudo tee /sys/class/leds/led1/brightness > /dev/null && echo 1 | sudo tee /sys/class/leds/led0/brightness"

[Install]
WantedBy=multi-user.target

To Start Script On Boot:

sudo systemctl enable disable-led.service

To Enable Onboard LEDs Again:

sudo systemctl stop disable-led.service