Quick answer: I think you can use the DOM-API… here you can open the report-template (at runtime ::LlDomOpenProject()…), iterate through all ‘objects’ and modify the Font-Properties. Maybe the tool ‘DOMViewer’ (lldomviewXX.exe) can help you to visualize the DOM-Properties of each DOM-Object.
Quicker solution: Try to make a “Search & Replace” inside of the report-template.