I think that spouses tend to change each other. Being around me changed my husband and being around him changed me. Both for the better, I think

But I don't think there's anything wrong with changing, even openly requesting a change. For instance, my husband was initially extremely NOT understanding about mental illness, so when I got diagnosed with PPD and PTSD, we had friction. I told him that he needed to educate himself and sympathize with me, so we went to seven months of marital counseling. And of course I expected him to change that negative mentality-- I don't think that's unfair of me. And he loves me, so he put in a ton of effort and grew as a person so that he could make me happy. I used to be extremely harsh and unemotional with him, but I learned that he needed some softening in my words and thoughtful gestures in his love language (referring to The Five Love Languages). So I grew for him as well.
If I were to get married and go twenty years without growing or changing (or hell, living unmarried and going without growing or changing), I would feel stagnant and like a failure. Live is meant to be a constantly teaching, changing, fluid experience.
Agree with this, too. Circumstances change, people have to adapt to them. But to go into a relationship expecting the other to change (or, conversely, promising that YOU will change) is misguided, at best. And it's always possible to change one's behavior without changing the basic nature of oneself.....