I Nailed it finaly !
Prior to ANY use of FsmBuilder, one needs to use FsmEditor.SelectFsm( YourFSM );
There is an internal static pointer to currently selected Fsm.. just took me 1 week to find what call sets that.
For future users :
Should you want to create your own Fsm, derived directly from a PlayMakerFsm object, you need to (in this order):
1/ AddComponent<YourFSM >()
2/ FsmEditor.SelectFsm( YourFSM );
3/ Use all FsmBuilder static and methods for your purpose.
Do not :
Create objects manualy to then append them to YourFSM.Fsm, it won't work.
Future Api improvements :
1/ Put Fsm as a read/write instead if just a read function ?
2/ Make the FsmBuild function self contained, with all responsabilities on its side.
I might say it is a bit akward to go through the view, to set the model rigfht now.