I'm slightly confused. I have a full grid, the quotation and a pretty representation using 28 cells as per the Down instructions. But, the quotation (which I've checked in three different sources) leaves me with six Across clues, not four. Three of these six clues occur immediately before the last word of the quotation. I'm happy that four of my six clues do not have misprints so I don't know what the other two are (I can't see their full wordplay).
I also don't understand the third sentence of the preamble which relates to the four Across clues. I've entered the solutions from the clues as the preamble tell us to do but I can't see any subsequent 'thematic alterations' that could be done. If I have the correct four words, they just seem random to me.
As no-one else has commented on these, I assume that I've done something wrong or just misunderstood part of the endgame.