Modifying Patch Creation Properties (.pcp) file programmatically?

Is there a way to script the complete process o开发者_StackOverflowf a hotfix build using msiexec.exe and msimsp.exe with a Patch Creation Properties file?

I use msiexec.exe to create network installations of the before and after msi files, Orca to create a .pcp file, and msimsp.exe to create the patch file.

I have been following the steps in these two articles:

How to create installation patches for VS.NET deployment projects

Patching and Updates

Suppose I had created a patch from 1.0 to 1.1 and now want to create a patch from 1.1 to 1.2 (or 1.0 to 1.2). I would like to reuse the .pcp file I created with Orca, but any modifications to that file should be done through scripting (e.g. VBScript) rather than someone having to open it in Orca again. From what I understand, I have to - at the very least - change the PatchGUID value.

How do I make such a modification using scripting?

Why not the WIX way: http://wix.sourceforge.net/manual-wix3/patch_building.htm