At the very perimeter of this question it's important to remember that:
... God himself, who makes the revelation and can neither deceive nor be deceived.
First Vatican Council Decree
So, if he didn't deceive us by His regret at making us, then He really did regret making us.
Regret, however, is a feeling - not an action, and one thing they tell you in Catholic Marriage class is that feelings are never wrong! I'm not sure if this applies to God, but the story of the Bible is a love story between God and His Spouse the Church. Sometimes even spouses regret at having gotten married, but it doesn't make them liars all the way back to their wedding vows. Neither does it make God a liar for having created man for having regretted creating them. Nor does it mean He made a mistake. Nor does it mean He wouldn't do it the same way if He could (and He could) do it all over again.
God also appears to have changed His mind, for the better - but to no different end - in saying He'd spare Sodom if a few good people could be found there. In fact, what is the point of prayer, if not to change God's mind about the natural course of events He set in place or the divine judgment He revealed to the prophets.
“Miracles happen. But they need prayer! A courageous prayer, that struggles for that miracle. Not like those prayers of courtesy: Ah, I will pray for you! Followed by one Our Father, a Hail Mary and then I forget. No! It takes a brave prayer like that of Abraham who was struggling with the Lord to save the city, like that of Moses who prayed, his hands held high when he grew weary...”.
Pope Francis - May 20 2013
I'll give you that Numbers and Genesis seem to contradict each other here. I'm surprised they didn't have intratext notes for those two verses which pretty clearly fit together, but the footnotes in the NAB for Genesis 6:6 are as follows:
the expression can be misleading in English, for “heart” in Hebrew is the seat of memory and judgment rather than emotion. The phrase is actually parallel to the first half of the sentence
And Numbers 19:23 is as follows:
God is not a human being who speaks falsely, nor a mortal, who feels regret.
And in the context of the "feeling" regret vs having regret contradicts my earlier opinions about regret being a feeling.
A corollary of these contradictions can be found in St. Thomas Aquinas' Summa articles concerning tempting God. He states:
It is forbidden in God's Law, for it is written (Deuteronomy 6:10): "Thou shalt not tempt the Lord thy God."
and then goes on to enumerate the ways God favors those who pray without tempting Him.
Similarly, God wants us to know that He is unchanging, while still letting us know that He loves us too much to be a stickler about it.