@mikeisfly:
I'm assuming I could take a full backup file and edit it to my needs and restore that without corrupting the whole system right? Assuming I don't make any mistakes.
That's the only way it can reasonably work. What you want is the separation of Interface Assignments (e.g. LAN is em0, WAN is em1) and "the rest". So you can prepare a new box with Interface Assignments (e.g. LAN: ra0, WAN: ra1) and pull all the additional information from an Interface-Assigment-less configuration file.
Well, it should work in such a simple case. But what about VLANs? Ouch. An automated decision which VLANs to keep and which to ignore would be quite complex, if not immpossible.
The only safe way is to manually edit the configuration file with a text editor before restoring it on the target machine. It's quite simple, in most cases. In some more complex cases, I did a partial pre-configuration of the target machine and then manually merged the config fiels from the old and the new machine.