Changing the name of a player you want to sell, seems that working better than giving him a special ability
my alt. team, Asteras, lv2 - after I played in CH.L. final, sold 3 6* players (with low q) to lv3 team
very easy after changing their names
my alt.team Artemis, lv2 - was difficult to sell a guy named Guschin but after renamed him (also) as Ozil, the job was done
Well, I wasn't sure if this trick is still working in higher levels like 12 of my main team ...
It does - after rename my player Emerson (3 auctions without result) , as Ozil (again) , I sold him.