Blasphemy is a much misused term. There are a lot of definitions out there, but they all pretty much break down like this:
blasphemy (noun)
1. blasphemous language (expressing disrespect for God or for something sacred)
2. blasphemous behavior; the act of depriving something of its sacred character; "desecration of the Holy Sabbath" [syn: profanation]
"blasphemy." WordNet® 2.1. Princeton University. 08 Feb. 2007. <Dictionary.com http://dictionary.reference.com/browse/blasphemy>.
Unless the character is saying disrespectful things about God, it isn't blasphemy. However attributing words to God that he didn't say would be considered heresy.
2 Peter 2:1 But there were false prophets also among the people, even as there shall be false teachers among you, who privily shall bring in damnable heresies, even denying the Lord that bought them, and bring upon themselves swift destruction.
Whether you personally are committing heresy would depend on whether your message is to claim that God actually said the things the prophet said. However, if you believe in God, I can't imagine that you'd do that. If you don't believe in God, I can't imagine you'd care.