Guy Betsy.....
I am going to Rio Thursday on a converted revenue seat....but since I "usually" book my award tickets way in advance....getting a seat has never been a problem for me. This is the first time that I've had AC convert a revenue seat for me.
Now having done that.....I wanted to make a change 3 weeks ago and the agent said politely to "forget about it" as ever flight was "oversold" by 30+ pax and changes were impossible as a result. If it wasn't oversold....it would have been no problem to get whatever I wanted.
It's a dubious benefit at best IMHO.