Hi,
ok, what plugins are you using? prime31 gameCenter? I don't have this one unfortunatly.
as far as implement c# action callback. you simply need to register a function within your playmaker custom action to that c# action.
something like
GameCenterManager.profilePhotoLoaded += ProfilePhotoLoadedCallBack;
where ProfilePhotoLoadedCallBack is a function, within that function, you can then set ProfilePhoto.Value to true or false depending on the result of the profilePhotoLoaded action call back.
you should also look up the web for c# examples on event action handling, or simply the example from gameCenter itself, Surely it's implementing somehow this action in a sample right?
bye,
Jean