[oXygen-user] Overriding Schematron process-assert template during XML validation

Hi, Is there a way to make Oxygen's RelaxNG/Schematron validation of XML files pick up my customizations of templates like process-assert or process-message? I know how to make this work outside of Oxygen, but I'm having trouble finding the right hooks in Oxygen (and tinkering with oxygen.jar seems like a really bad idea). Do I extend the Schematron framework, or is that used only for editing Schematron source files? Thanks, Amanda