The skin really looks fantastic! Thanks for creating it.
On PC you can use /Icarus_data/Icarus2SkinSmall.png and /Icarus_data/Icarus2SkinLarge.png to import custom skins . The files are loaded when the plugin is loaded. In Icarus 2 only up to 2 skins can be overwritten. Please note that this is a hidden feature for development and not officially supported.
Future PC versions will also support /Icarus_data/Icarus2SkinSmaller.png
On Mac the custom skins most likely will work with Icarus2.0. But they might not longer work with future updates, because Apple made the Notarisation more strict in 2020. As a result plugins might fail scanning and be not longer visible in some hosts when you change the resources of plugins which have been Notarized after 2020. Then it is possible that the VST still works, but the Audiunit not. I think there existis a workaround to switch off the Notarisation from the user-side, but do not longer remember how.
Markus