It is possible to change the panel lights within the terrain control module or are they LED's?

They are LED's integrated into a circuit board, if yours is missing some illumination it has been reported that the circuit board has sometimes unclipped and dropped away.

it is possible to change the surface mount LEDs, I did the full dashboard in my last Astra from dodgy orange to blue and white... but unless you know what you're doing it's not recommended that you try it at all

a decent electrician that it used to working on small components should be able to fix any blown LEDs

Thanks for your replies. I will have a quick peek to see if the PCB is in place, assuming you can when the control is removed. Otherwise I shall just 'suck it up'...............but I do like everything to work!