Writing a mood is probably to make others or someone pay attention to themselves, but generally it doesn't refer to anyone (especially who you are writing for, that is, you are already in love, and generally you won't write anything but your own happiness)

Updating the screen name is either for freshness or to attract attention. Generally, some people often change their names when they first start playing or find Q interesting, but as you said, their moods often change. I guess they want others or someone to pay attention to themselves.