You mentioned UAC protection. Have you tried to run MSFS Livery Tools as administrator? If this works, that is the problem I have to solve. Simply copying the folder should not change permissions, but it may allow you to override this setting. I have moved all my packages to a custom location, and so I can’t test this.
One note: you probably have read permission to those files, and this should be enough. You only need write permission to your project and packaging folders.