You can, indeed, reshuffle at will.
Bring up the context menu in the WPS, select the 'Playlists' entry, and then select 'Reshuffle'.
You can also use the 'Insert Next' playlist option to achieve you other goal by bringing up the context menu on the track you would like to listen to and then selecting 'Current Playlist - Insert Next'.
And...that's it.
The manual does indeed describe both these functions, and their usage, but it may have been non-obvious to you that these were the functions you were in fact looking for.
[Saint]