Hello.

I suggest you to use XWiki and to add the object directly with the UI. 
Then: 
- you can export the page as a XAR
- you decompress the XAR (which is nothing but a ZIP file)
- you open the XML file that describes the page
- you merge this XML with the one you have in your xwiki-platform repository (only the lines concerning this new object).

Then your guid issue will be fixed :) This is my own workflow when I need to modify XWiki page.

Thanks,
Guillaume