For award tickets, AFKL rebook you without troubles when it's on their own flights. Troubles begin when some flights are on partner airlines because they don't control the award inventory for FB members on partner airlines, even within Skyteam or old-time JV partners like DL. There shouldn't be any troubles normally, but in practice it's always complicated because AFKL agents just follow the computer saying no seats available and don't want to deal with the operating partner. Skyteam alliance has failed miserably to that respect to provide seamless travel because traveller impacted always has to fight to get rebooked. There is no magic phrase to use but HUCA is usually the best strategy if you speak to an incompetent or lazy agent.