The difference is that a "patch" implies that it is added to exterior content which means that the question of copyright infringement passes to how that exterio

The difference is that a "patch" implies that it is added to exterior content which means that the question of copyright infringement passes to how that exterior content was obtained. Patching pirated work is still piracy, but patching work you have purchased legitimately (or were given by the copyright holder, such as a web page) is not piracy.