Yeah, absolutely I do.
I think the idea that one could change in a way that is so intrinsic, e.g. discovering the capacity for mercy, and continue to have the same social function, e.g. continue to be that Gunlugger killing machine, is a naive perspective on human nature. Could be I'm putting a lot more weight on what moves mean for a character than you are, but based on my experiences, that's what I think.
Changing behaviour is incredibly difficult if you stay in the place that encourages it. You're never going to get clean if you continue to hang out with junkies. On the other side of the coin, a drastic shift in perspective can result in the inability to continue on in a certain position. It's pretty hard to continue being a combat-deployed soldier after you decide you're not going to shoot at people anymore.
On the other hand, I think you could do a lot in terms of role-playing around the problem before demanding that the rules be changed immediately. If you have Merciless and there's a specific situation where you don't want to be dealing out 3-harm all over the place, I'd suggest trying to find a solution through role-play before you start changing the rules. You still have plenty of opportunities to deal out only 1-harm! Finding them is part of playing that particular character in a moment of crisis.
Also, I wasn't suggesting switching to the same playbook, that was Shreyas. I think that's totally weird. Although I could see a Gunlugger giving up all his bad-ass moves to become a Driver or something, and then returning to the Gunlugger playbook later when he just couldn't stay pacifist. That would be very Jimmy McNulty of him.