Are you definitely using the very latest version of JUCE? I just tried building the DSPModulePluginDemo, using the Projucer’s Xcode and VS2019 exporters. I added JucePlugin_AAX_Chunk_Identifier='blah' to the preprocessor definitions of both exporters. The builds completed successfully after that. Putting a message pragma in the AAX_Wrapper.cpp shows that the value set in the Projucer is definitely visible.