@jeffy162: You're right, I will try to remember that
@Banknorris: Thanks! That's a good workaround actually, doesn't solve entirely the problem since, like @Ammako said, some people might have used all of their general macro slots (not me, so I'll try doing that ^^).
@Ammako: So I just did the test on my DK: row 3 of honor talents contains 2 spells (Dark Simulacrum & Anti-Magic zone), I put the 2 of them in a bar with Frost spec, outside of a battleground (both spells disabled, one of them having the mention "Honor Talent" in its tooltip). I switch to Unholy spec (I even tried to reload UI and logout), go back to frost spec and the spells are still there, same if I try with PvE talents!
So the games allows that, but maybe there's no way to do it through the API
I'll still try to find the proper solution while using @Banknorris workaround for the time being ^^ but if anyone has an idea, please tell!