Good omens is Blasphemy
Well, when we’re doing it right, anyway.
Unless of course, it’s Ineffable, in which case it can’t be blasphemous, because it’s all part of the plan.
But like Aziraphale and Crowley argued in season 1, given that the ineffable plan is, by nature, ineffable, it excludes the possibility of knowingly defying it, and that of being caught defying it.
Therefore nothing can be blasphemous, really.
There go my weekend plans…