I found out that to access the Playback Settings, it is actually necessary to go through the Level Sequence Actor. When a Level Sequence Player is created, it creates also an Actor at the same time, which can be retrieved.
And so I did ! And so now can I access the Playback Settings. Yay !!!
However … However, the settings are kept inside a Structure, therefore it is necessary to go through an external node called Set members in MovieSceneSequencePlaybackSettings to modify the settings.
Warning reads : The Playback Settings is a Read Only property and can not be modified directly.
And there is the problem ! The Playback Settings of the Level Sequence Actor are Const and Read Only. Therefore, they can’t be modified, even through the node meant for that purpose … .
But why ? Just why ? Is this normal ? Why can these settings absolutely not be modified at runtime ? I don’t get it.