@Eskano Of course, just add a button into the panel, and in the button callback, just use Panel.showControl(false);
Well, if you look at the code, you can see that the panel is showing after 3 sec, then the timer stops in its own callback, hence will not popup again if you close it. (unless you tell him to do so in the close button callback...)
By instance, do you mean plugin or panel instance?
The panel will show again after 3 sec when you relaunch the plugin. If you want it to appear only once when you launch the plugin for the first time and not after that, you'll need to store a flag in an external file using dumpAsJSON/loadFromJSON.
@TNTHM For this, you need to combine what I explained above with: https://forum.hise.audio/topic/1204/simple-copy-protection-done-right