That’s not my experience- I had a family trip (4 of us) MAD-LHR Avios redemption in CE earlier this summer, which they changed (with no change fee, only the additional Avios) to ACE-LHR at my request. Then I changed it again to MAD-LHR but for a different date than the original. I’m regular Gold, not GGL.
I thought it was strange it didn't apply to awards, but since I was on the phone with YouFirst and it was a UK call center, I thought they would be knowledgeable about it. The agent seemed competent but I didn't know for sure whether he was wrong...will call YouFirst again to inquire about the FTV.