Could you give me some more information about what context you are expecting to see the property customization appear in? The customizations are specifically only for the details panels and a details panel does not generally show UFUNCTIONs.
The PropertyModule customizations only pertain to the PropertyModule - this module is responsible only for details panels.
To customize the pins in a BP graphs, there is a different mechanism. FGraphPanelPinFactory is the class that you can subclass and register with `FEdGraphUtilities::RegisterVisualPinFactory`. When the GraphEditor generates pins, it will iterate all registered factories and return the first factory that is able to generate the desired pin. It will be up to your implementation to inspect the UEdGraphPin to determine what type it was and if it matched the enum type that you want to customize. If it all matches, then the factory can generate a SGraphPin widget that is appropriate for the enum that you would like to customize.
One place I would look for examples in the code is FNiagaraScriptGraphPanelPinFactory which registers customizations for several custom types that Niagara defines.