Fixups are application layer intelligence about specific protocols.
What you need is a access-list entry in your ACL for the outside, outside-acl in my example. Assuming there is a server at private address X on the inside, and you want to access it from the outside using address Y. You would need something like this:
static (inside,outside) Y X netmask 255.255.255.255
access-list outside-acl permit tcp any host Y eq 450
You'll need to clear the translation for that host if you're adding the static statement as part of this new configuration.
clear xlate local X (X is the server address)
-S
