Missing parameter LED_MODE in rover 2.51

Hello
I am new here and ask for your help.
I need some external LEDs on my model (motor, armed, GPS). Using Ardupilot 2.8, I found some useful instructions on how to configure LED_MODE parameter. My problem: I cant find it in the full parameter list.
Is there a solution to this problem?
Many thanks for your help!!!
Sailor2