I need to change format of all usernames in KanBo.

In KanBo it is possible to change the user ID to anything. It is just an identifier. If you change it in the AD or wherever then you just have to change it in 2 tables in 2 databases in KanBo.

You can change the content of the login fields in the Databases - it will work. Make sure you do it in the Profile database and in the Content database.

LoginName table is used to uniquely map given sharepoint identity as user in KanBo

Users.ProfileKey field is used to fetch and create user's profile from Profiles database. Importing the user into instance will use his/her current login name in sharepoint as a ProfileKey - in case of using multiple instances changing LoginName might not be enough and adjusting ProfileKey to the new login would be a good practice in case the new instance is created in the future.