I'm a few versions behind you, but you could search for "XMLPackage.OrderReceipt" if you have source code you'll find where it is referenced. I know it's called from the Order module. XMLPackage.OrderReceipt is the AppConfig Name and the config value is notification.receipt.xml.config - the config value is the first parameter in the function call AppLogic.RunXmlPackage()
You have to understand the XSLT and java to make modifications to the file.
Hope this helps.
Parrothead
"I'd rather die while I'm livin' than live while I'm dead."