When trying to change the alias username under aliases db list the username it looks like the value is being casted to an int before deciding to update the value. So changing 123456789 to 0123456789 or +123456789 will fail since 123456789==0123456789==+123456789 from a numeric point of view.
workaround is to change 123456789 to something else (foo) and then the number with the desired prefix.