Replacing a File in an existing Package

[pilotError]

I have a package that I want to replace a file in.

 

How do I do that.

 

Package name: Essentials.pkg

Modified File Name: PlatformSupport.plist

Location in Package: /System/Library/CoreServices

 

I tried using ditto

 

ditto -c PlatformSupport.plist Essentials.pkg/System/Library/CoreServices

 

but I get the error:

 

ditto: can't create parent directory for Essentials.pkg/System/Library/CoreServices

 

Thanks for your help...