I think I recall doing some personality forcing work with Bune (Ian) pre-integration, which is relatively recently (~a yearish). I remember Bune saying what traits he wanted to try and what he wanted to reject. I think it had mixed results iirc, but I don't think it was a super serious attempt? I would have to look back at the logs.
Ironically it might be easier to let go of an undesirable trait if they're an older tulpa. It's sort of like looking back on your old posts and realizing how cringe they are- you recognize the behavior or traits you don't like and reject them. However, if you don't have much confidence in claiming other qualities as "you", it may be ineffective.
Personality forcing is an expectation based approach that works because it helps you associate what behaviors/traits are considered "you" and what is not, and the timing matters. A super fresh young tulpa sometimes has no associations or expectations, but an underdeveloped tulpa may be more insecure and reject anything that threatens their weak sense of self. I think it's worth noting several of my headmates made big deviations once they had a broader sense of self to work with.
Ultimately, I think it can work, but it may not be super effective if the headmate finds change threatening to their sense of self. I think given the circumstances, I wouldn't be surprised if that's why Bune (Ian) didn't continue this approach- he was not ready to embrace a big change despite ironically looking for one.
Looks at logs ah, it looks like Bune (Ian) decided to integrate instead of going with the personality forcing route. I do remember sitting down with him at one point though, and he did report a weak sense of self (edited)