Yes, this actually happened, according to French journalists Roger Faligot and Pascal Krop, both of whom were mainstream journalists and specialized in French counterinsurgency and covert operations.
Here is the claim in English, contextualized as part of France's operations against Guinea:
From E. Schmidt, Cold War and Decolonization in Guinea, 1946–1958, 171–172.
The citation for the counterfeiting goes to Roger Faligot and Pascal Krop, La Piscine: Les Services Secrets Français, 1944–1984 (Paris: Éditions du Seuil, 1985), 246–47, which I do not have on hand.
edit, 2021: Here is the passage in question.
The quotation seems to be from Col. Tristan Richard, a secret service agent who was confident enough in his own reputation to sue his own subordinate in 1981, claiming defamation.