@sjaehn Code just uses LV2 mechanisms for informing the host of changes, and receiving back those again.
There is nothing extra to do on the plugin-side for this, we get it "for free".

I could have the same in Carla when having Carla-Control on a remote machine, but did not bother setting up custom GUI support for that yet.

Note the same is possible in VST3 too, it also has host-provided message passing for UIs to communicate with the DSP side and vice-versa. No host I know handles it though