The rest of that SAME verse implies that when God says he's going to do something he doesn't change his mind. [...] One of these scriptures has to be wrong. Either it's the one that says god doesn't change his mind, or it's the ones that say he does.
I think you missed the reason why they cited that scripture. It's precisely BECAUSE it seems to conflict with the "regret" scriptures. In other words, the scriptures don't conflict, it's your understanding of the word "regret" that's clearly wrong. QED. Signed, The Watchtower.