Num 23:19, "God is not a man, that He should lie, Nor a son of man, that He should repent.“
1Sam 15:29, "And also the Strength of Israel will not lie nor relent. For He is not a man, that He should relent.”
Relent or repent, the Heb. term is the same; and also the same term as Gen.6:6, rendered "sorry" (repentant)
The above is a kind of self-defining statement (repeated 2X) from our God about himself, his character and behavior; especially as it compares to man and his typical ways. We should not receive Gen.6:6 as if it contradicted the explicit refusal of the idea found elsewhere. We should interpret Gen.6:6 as anthropomorphic (-pathic) language; or more precisely as expressive of the aggrieved quality of the divine heart, because sin has that relation to the divine holiness.
See Hos.11:8 or Ezk 33:11 (among many) for consistent expressions of how God "reacts" to sin (when in reality he doesn't "react" but is forever the Actor). It seems to us God changes course when we change course, but the reality is that the change is all ours, as we become conformed to our relation to him either in grace or wrath.
God cannot regard sin positively, but negatively; which regard is variously described using our human emotional categories (since God, who is very different Being from us, accommodates himself to our frame of reference for the sake of communication).