Hi,
As far I know we can create a user (on client UI) through two ways like through User import and new user. With both the approaches userId and username accommodates 8 and 40 chars respectively and when I tried to use import function by providing username with the same length as "hassan.raza.rules" i.e 17 characters, could not find any truncation after creation. So, I feel you can use the username without any change.