New user name was introduced in 2.5.2.p1-9.
See https://bugzilla.redhat.com/124510 for details.

Amanda's RPMs contain scriptlets for automatic
transition to new 'amandabackup' user name.
Update of files /etc/amanda/*/amanda.conf,
/var/lib/amanda/.amandahosts, /etc/xinetd.d/amanda
as well as renaming /var/spool/cron/amanda
is handled by these scriptlets. Original files
are backed up with .usernameupdate extension.

Other needed changes must be done manually...