Section id is based on the name you chose for the character. It is possible to add extra letters/symbols to change it up sometimes. Only 9 letters display in game but it lets you enter 10, so if you need to you can do something like 'Ranger X' and no one would see the X; there is a section id calculator to help players determine their name. There is also the /changesectionid command which players can use once every 3 months.