You can change any award for EUR 40, but in your specific case, the companion award would then change into 2 normal awards, so LH would have to pull the additonal miles.

Of course, there's a chance M&M/LH might not realize the sinister plot behind your change and simply forget pulling the miles - I have no clue about the sophistication of their award booking system ot their CSAs in this regard. My guess is that they'll see it, as companion awards are certainly booked under ONE itinerary with ONE single Amadeus booking code. So your booking needs to be split up into TWO seperate itineraries and Amadeus codes.

The one thing that's clear is that you are deliberately trying to fool them. Which, should they catch you, I'm sure you will vividly deny.