[@Klomster]
There is a leeway. If your character were to acquire an artifact that belonged to a dead god (probably one slain by Justinian) and that artifact contains the dead god's magic, your mortal could inherit that magic. After this, he would have to perform a ritual of self-sacrifice. (To become a god, he will have to die by default.) And once dead, if his soul is bound to the artifact he could become a Red God. Not a powerful one, though. He'd have to play it safe all the way, because Justinian is a tremendous and very active foe.