Change Postfix to accept incoming mail on port 1054 or other but send outgoing mail on 25

modify /etc/services
add a new service (say smtp2) with port 1054.
leave smtp at 25

modify /etc/postfix./master.cf
change the line that reads

"smtp inet n - n - - smtpd"
to
"smtp2 inet n - n - - smtpd"

restart postfix
postfix reload