I'm glad you got the exec working.

I can't help with PHP because I have never used that library, but you asked about changing the value names... The only way to change the names is to override the exiftool defaults by defining custom tags or modifying the exiftool modules directly. The only disadvantage to modifying the modules is that it makes updating to the current version of exiftool difficult, but they are easy to modify since they are all plain text files.

- Phil