In many biblical instances, we see where God purposes to do something and then repents of this. In fact we see where God implores a person or people to change their ways so that He can repent of what He has purposed. For example, in Jeremiah 26, God sent his prophet to prophesy against the Israelites an incoming doom. This was because the people had failed God. Yet, the prophesy also said that God would repent of his decision to destroy them should they change their ways for good.
Therefore now amend your ways and your doings, and obey the voice of the Lord your God; and the Lord will repent him of the evil that he hath pronounced against you – Jeremiah 26:13
If so be they will hearken, and turn every man from his evil way, that I may repent me of the evil, which I purpose to do unto them because of the evil of their doings. – Jeremiah 26:3