guys, the solution is obvious: have two states stored persistently: the fullscreen state in normal mode and the fullscreen state in guideance mode. So it's still possible to set guidance mode fullscreen by whatever complicated way thru menus or whatever, have only one button for guidance-off in guidance mode, and still get maximum flexibility.
Alternatively you can have a "config visible buttons" thing, just like you can configure your toolbar in any normal KDE program.

Sure there MUST NOT be anything like fullscreen mode for any state hardcoded.

/j