This puzzle was intended to be formatted as a PDF; the puzzle PDF is available on Dropbox, and a screenshot of said PDF is hosted on Imgur. If you'd like to solve digitally, there is also a template Google sheet.
The referenced puzzle is available here; no knowledge of it is necessary to solve this puzzle.
This puzzle is an entry in Fortnightly Topic Challenge 46, "Tales from the Cryptic".
Not Bluebeard's Castle
In Bela Bartók's opera, Bluebeard's Castle, a woman enters a dark and mysterious manor for the first time. This manor has several doors that the owner of the manor claims should never be opened, but the woman's curiosity gets the best of her; she opens all the doors and makes a gruesome discovery.
...But there's already a cryptic crossword with that theme, so we'll have to make do with a substitute. This puzzle is based on a similar work that also contains the described events.
The unclued top row of the grid gives the title of the work. Each Down answer must be modified in accordance with this title, producing new words each time (one hyphenated, one prefix, and three proper nouns).
Unlike Bluebeard's Castle, after the "gruesome discovery" in this work, the performance continues. The protagonist's reaction to the discovery has briefly affected 7 of the Across clues.
The first letters of these clues (in an appropriate order) will describe how both this puzzle and this work set appropriate expectations for the future, each in two different ways.
The unclued bottom row both describes what happened in the manor before the discovery, and explains “the protagonist's reaction” in more detail.
1. (see instructions)
12. Shannon's location is "engaged in wandering" (4)
13. First-class defamation backfiring in Russian parliament (4)
14. Called southern Asian city restaurant (4)
15. Psychotic Charlie is biting John (4)
16. Observe "quitting at 02:01" in declaration of innocence (3, 1)
18. Medals of doctor Tyson (5)
20. Radical town around Eaton (5)
21. Riddle: "I'm a Democrat, but not liberal..." (5)
23. Evan Dalton's secretly an anonymous artist (6)
24. Once again, look at red ear, award (6)
25. Ensure Steve's tool is not even taken (3,2)
26. 1970 maybe was amazing, as I hear (5)
28. A member of tribal pro-ent flank (5)
32. Falls out of the ranks (4)
35. Tropical fruit sated poorly when sun was out (4)
38. Near Kauai, island's oppressive authoritarian has uprooted forest areas (4)
39. A bit cross after being flipped (having had no temper initially) (4)
40. End to tedium not found in methods of operating things written by a list (4)
41. (see instructions)
1. Rush is a band
2. Expression of discontent with rag edited by Henry
3. Talk about concealing American records
4. Grace's death -- that hurts
5. Word to deny the writer and reader's intellect
6. Character from dogmatic Alaskan city brought up evil spirit
7. Close on new car, disheartened
8. I find I am cut
9. Source of glitch about Null Island
10. Small mountain is not extremely cold
11. Orc in LOTR violently struck nationalist symbol looking like the flag of Egypt
17. Small marine predator from weir that's been damaged
19. In olden times, you like votes in favor
20. Houston group's detailed piercing
22. Stocker pal?
27. In court, regret having created small jar
28. Kitschy down fabric
29. Saw card with moon sitting on top of menu
30. Loud guy to be braided in ad
31. Types answer after stress
33. Mountain in Greece obscuring some smaller adjacent peaks
34. Clandestinely transmute something erotic
36. Greek goddess is discovered to be back
37. What once was vacant Exeter Street