Can the font be set via AppManager? https://sdkdocs.roku.com/display/sdkdoc/roAppManager The Application Manager APIs set application level attributes, which mostly affect the look-and-feel of the application. The use of screen styles gives each application a consistent look-and-feel, but it's often desirable to customize attributes such as colors, fonts, and logos for each application.
roAppManager can control the color of the system font in some pre-Scenegraph components, but not the font itself. If you really want to set a font you would need to use SceneGraph, roScreen or roImageCanvas screen types and load a .TTF or .OTF font in your app or download it to tmp:/ before instantiating it.