Full grid OK and highlighted what is indicated by the down clue corrections BUT can't make out what the across clue extra words are indicating. Any nudges welcome.
The instruction parses as 6, 7, 3, 3, 5, 4. If you are familiar with the source material yo;ll know which of the shaded characters is actually the "5,4"
I must be very dim today (not helped by a numerical in another place). I can get the 6, … 5,4 I think, but the 7,3,3 elude me, even though I know the story.
The preamble specifically mentions letters from the extra words, not the extra words themselves. Word breaks for the instruction are not the same as the ends of the extra words.