Plugins can be loaded before a World / Level is loaded, and worlds/levels may unload/reload without the plugin being notified, so what you say you want to do wouldn’t work out well.
Why does your code need to be an Actor? Does it really need to be an Actor in every world? Even if that world is just, say, a “welcome to the game” menu?
In general, if you need a particular actor in a particular world, you add it to the world. And if you don’t need it, you don’t add it.
If your plugin needs to “run code on tick,” it can add itself as a tick listener, even without being an Actor. See for example FTickFunction for a place to start.