Karl,
I am also using version 4.5.3.1, but under Windows XP Pro.
The renaming code is exactly the same on both platforms (the Mac uses the Windows code.)
Are you sure your model names match exactly the codes in your code replacement file?
One easy way of checking this is to set your Info Text to include the {model} variable and then turn on the Info Tooltips on the View menu. Then when you hover over each thumbnail you'll see the value of the model for each photo. The model needs to exactly match the code in the Code Replacement file in order to work. Otherwise no replacement is performed and you'll see your delimiter characters when the Rename preview appears.
HTH,
-Kirk