Pour info, j'avais posé la question par mail à FFG au moment de la discussion, et j'ai reçu la réponse de Nate French qui confirme bien la réponse obtenue entretemps sur cardgamedb:
Question: "After the use of Elemental Fury, the "contested ring" is changed. Is the "declared ring" changed too or does it stay the same? Ex: My opponent declares a Void conflict on 1 of my provinces. I reveal Elemental Fury and switch the contested ring to Fire. Am I able to play Mantra of Fire or is the "declared ring" still Void while the "contested ring" is Fire?"
Réponse: "In your example, the declared Ring is still Void, and the contested ring is now Fire. You cannot play Mantra of Fire in this situation."
