Changing a username for an account with WHM or
Cpanel usually results in havoc.
In a shared scenario the username is appended to
databasename.
If your database is name drupal then it
becomes username_drupal
and since your password is attached to a username rather than inherited in
some way.
In other words you create a username
when you create a new account...then a cpanel password is assigned to to that
username or account.
as for the database:
My Cpanel will not allow me to change successfully a username.
I must create a new account and never use the old username again. If
I want to use something similar, I change the last letter to a number such as
olduser1...usually 8 letters or less. and assign any password to it.
then each database becomes olduser1_drupal and then I
create a database username such as asdf123 and use it for that and all other
databases on that account.
Hope this helps
Russ Griechen