So the character is a godless athiest that has suddenly gained stats that rival or, probably, surpass the gods themselves?
Here's how I would play it out. He casts his epic spells, gaining an instant, unfathomably high boost in his perception of the universe. Play out the Transcendent nature of the change (go for the 2001-esque "Oh my god, it's full of stars!" kind of feeling of awe and wonder). Mere moments after attaining what is essentially godhood, the character will percieve all the secrets of the multiverse. This will reveal several very relevant things to him:
First, he is now a threat to the gods in a way he never was before. And he has the Charisma to lure away huge chunks of their follower-base.
Second, he realizes the gods are inevitably going to come gunning for him. All of them. With a serious attitude.
Third, while his intellect is titanic, there's no way he can make himself powerful enough to survive that inevitable confrontation with the gods.
Realizing all this in the first moment after attaining his transcendant state, he makes a change to his own mind, so that he retains all his vast, cosmic insight, but can't access it on a conscious level. He might not know why he's doing certain things, or why people are reacting so well to him, but it still happens. No longer an immediate threat to the gods, he can survive long enough to do what he needs to do, with only a fading memory of why it is so.
In other words, since the character built and cast the epic level spell, and the DM approved it, he should still get the benefits. But you can't roleplay that kind of mental state...without achieving Nirvana yourself. At which point, you've got better things to do than play D&D.
Or maybe you don't. Who can say?
