Genes don't work that way, there is no "God" gene. There is a biological mechanism to belief but genes are more sophisticated than This gene does this, this gene does that. It is possible they could rewire the brain to affect beliefs through surgery or drugs and they "could" do it with genetic tinkering but it is not as simple as editing out a line of code. That would lead to all sorts of unintended consequences as genetic material interacts at different times in different ways, at least that is my lay understanding from reading half a dozen or so books on genetics