How many times do you change your name in real life?
We see our online community very much like a real-life community, where we want members to get to know one another, form friendships, and help one another out with a lending hand or a supportive word. If someone is changing their name 3, 4, 5 times over the course of a year, it can get confusing to other members (as well as the community support team).
For every guideline, we're happy to make an exception when and where warranted. That's why we call them guidelines and not rules.

As long as there's a legitimate reason for needing to change your username again, we're happy to consider such exceptions.