Although I disliked Voyager for a variety of reasons, I have always liked Kate Mulgrew, and have always thought that she is a very attractive woman.
I like the later pictures and she looked good with her hair down. She looked older with her hair up, but with her hair up, she looks more commanding. I really liked seeing her with her hair down in a nightgown.
I am a teacher in China and one of the bosses is a woman who is about 35-40 years of age. She wears her hair short and tight with a small bun in back. In my opinion, it made her look ten years older than her age. For about a week, she let her hair down and she was quite cute and it took a decade off her age. Now for whatever reason, she had her hair back in "granny librarian" mode.
My take on it was that although having her hair down made her look younger and more attractive, it lost her sense of authority and respect of the workers. She wanted to look more formal and professional. Maybe she wears her hair down outside the office, who knows. But that is her look inside.
Probably the change was to make Kate look younger, softer and more attractive.