When is Theological Innovation NOT Acceptable?

(Knowing me, this will probably be a real short list, *grin*).

So let's dive in. When shouldn't we be creative when it comes to thinking about God, the Bible, Church, etc.?

1. When it's about sin and evil - sadly there were times when the Church endorsed evil like slavery, racism, sexism and genocide. May we never revert to these eras. Yet, I reckon our problem is that we often stop at the labelling of sin and don't think hard enough about what to do next (apart from condemnation)
   
2. When it's about historical events - I'm fine being creative with a question like, "What did Jesus believe about Himself?" but I'm not sure I've got patience for a statement like, "Jesus didn't exist." I also feel it'd be somewhat unhealthy for the Church to be overly creative with the facts and reality of Jesus' resurrection, though the work of historiography (and especially the Third Quest for the Historical Jesus) must go on, IMO

Toldcha I wouldn't have many bullet-points (smile). But what would you add? What would you consider a non-negotiable of the faith?