Since this is a discussion that requires knowing the mind of God, I wish to say at the outset that I don't know what I'm talking about and will not be held responsible for anything I say.
1. Since one of God's attributes is his immutability, and does not change his mind, to describe God as repenting cannot mean that he's changed his mind. That would be a change. So, repenting must mean something else when it's applied to God, different from when it's applied us
2. Maybe we ought to look for another definition of evil when trying to apply it to God's acts or decrees. In Isaiah 45:7, for example, the prophet quotes God as saying "....I make peace and create evil...." In this context, evil means calamity or disaster. And maybe God has the authority (because he's God) to define evil with regard to human behavior, but is not required to apply the term to himself for the same acts.
3. God's own nature demands that he disapprove of evil and sin, and approve of obedience. So I can't imagine God saying of the evil generation to which Noah preached, "well, that went well, don't you think?" No, it is God's nature to be grieved at sin. It is contrary to his nature for him to be happy about it.
4. We can't just explain everything by saying God knew it was going to happen. We also have to deal with the proposition that the reason God foresaw events is that he decided that the event would happen. In Acts 2:23, Peter said that Jesus was delivered up to be crucified "by the determined plan and foreknowledge of God..." And remember that this was planned in eternity past.
So it cannot be denied that God planned to use the evil acts of men to accomplish redemption for sinners. Not to over-ride those evil acts, but to include them as part of that "determined plan." Not only that, Peter described those who carried out the determined plan as wicked. Figure that one out.
5. And finally, we turn to Genesis 50;20, where Joseph told his brothers "As for you, you meant evil against me, but God meant it for good in order to bring about this present result, to preserve many people alive." God didn't just turn an evil act to good, he determined that the intended result (to preserve many people alive) would come from an evil act. Evil, that is, according to our definition.
Do I understand this stuff? Not a clue. I don't know how to make all this fit in some nice little system. But it cannot be denied because there it is, in black and white. God hates evil. God uses evil for good. God grieves at evil. God incorporates evil acts into his plan. Yet God does not sin.
Whew, my brain hurts.