Hello everyone. The obvious comment to make here is that this is a 23 puzzle …
The preamble:
The final grid represents a POSTER for 23. Eight answers to normal clues are to be amended before entry, leaving real words: (i) four answers in one half of the grid lose a letter; (ii) four answers in the other half need two letters of the alphabet to be swapped around. Remaining clues contain an extra word, first letters of which give an instruction for the entire grid. One entry in each half of the filled grid must be amended in the same way as before. Removing the letter leaves a space, but reveals the name of a protagonist changed as in the theme work; swapping two letters leaves one non-word answer, but reveals another protagonist’s name (both two words). The Chambers Dictionary (2016) is recommended; 37 Across is in Collins.
Quite a lengthy rubric, but the only part I needed to bear in mind initially was the extra words. I could remind myself of the alterations on finding a normal clue. The swapped-letter entries when they appeared in 8d and 15d were easy enough to sort out, as was 18a’s dropped letter. At this point I noticed that enumerations were of answers rather than entries, allowing the rest of the deletions to be readily identified. Everything came together smoothly, the grid fill and the emerging message:
COLOUR EACH HALF IN AN APPROPRIATE COLOUR
To work this out, I needed to complete 23, _ICKE_.
I scanned the grid for possible characters. Fortunately, being reasonably familiar with the theme, I noticed the character who would be my way in: GALINDA. In the musical WICKED, GALINDA changes her name to GLINDA, which makes perfect sense of the instruction to delete a letter. With a swap of letters, the ALPHABEt on the other side of the grid revealed her oppo ELPHABA.
The preamble tells us that each protagonist is two words, which was helpful as otherwise I would have completely missed the surnames of the characters, which had not stuck in my memory at all:
GLINDA UPLAND and ELPHAHA THROPP, from WICKED.
Neatly, each extends the length of the grid, and the only thing remaining was to colour in the space to match the colours from the original POSTER.
Thanks to the wizard Robyn – Wonderful!
If there is a setter’s blog for this puzzle it will be available after 9am here.

| # | ANSWER (ENTRY) |
Clue with definition underlined | |
| Explanation, with quoted indicators in italics and ANSWER letters in bold caps | |||
| Across | |||
| 1a | AGENDA | A [chauvinistic] male perhaps on the radio programme (6) | C |
| Sounds like (… on the radio) A plus GENDER (male perhaps) | |||
| 5a | SWEATS | Worries Harry wastes [opportunity] (6) | O |
| Make an anagram of (harry) WASTES | |||
| 9a | WARIER | More cautious 6, one replacing much [liquor] (6) | L |
| WAR[far]ER (6 – answer to 6d), I (one) replacing FAR (much) | |||
| 10a | PAELLA | Old man [ordered] two versions of the Spanish dish (6) | O |
| PA (old man) + EL and LA (two versions of the, Spanish) | |||
| 11a | ALIT | Got off trial easily, ignoring [unfair] rule (4) | U |
| An anagram of (… easily) T[r]IAL, ignoring R (rule) | |||
| 13a | BAUR | Scot’s [raunchy] joke you picked up in pub (4) | R |
| U (you picked up) in BAR (pub) | |||
| 14a | JPEG | Jack and Margaret [enlarged] image (4) | E |
| J (Jack) and PEG (Margaret) | |||
| 16a | RINGO | Bell [alarmed] old drummer (5) | A |
| RING (bell) + O (old) | |||
| 17a | FEHME | Charge to host royal in antiquated [charming] courts (5) | C |
| FEE (charge) containing (to host) HM (royal) | |||
| 18a | NAGANA NGANA |
Articles on horse disease affecting cattle (6) | |
| AN, A (articles) on NAG (horse) | |||
| 19a | NAWAB | Prince’s wife advanced wearing [heavy] collar (5) | H |
| W (wife) and A (advanced) in (wearing) NAB (collar) | |||
| 20a | ADOS | Notice huge [health] troubles (4) | H |
| AD (notice) + OS (huge) | |||
| 21a | ABAC | Early reader grasps answer [applying] maths aid (4) | A |
| ABC (early reader) surrounds (grasps) A (answer) | |||
| 24a | RUSTRE | Reddish-brown hue on [long] lozenge (6) | L |
| RUST (reddish-brown hue) + RE (on) | |||
| 27a | CRATUR | Celtic animal [flees] dog biting vermin (6) | F |
| CUR (dog) around (biting) RAT (vermin) | |||
| 29a | IMPLEACH | In books, entangle Liberal in [illegality] charge (8) | I |
| L (Liberal) in IMPEACH (charge) | |||
| 34a | SALUE SLUE |
For poet, what soldiers did in uniform during flogging (5) | |
| U (uniform) during SALE (flogging) | |||
| 35a | ERAS ARES |
Ages of meerkats occasionally neglected (4) | |
| mEeRkAtS omitting regular letters (occasionally neglected) | |||
| 36a | USTILAGO | Fungi suit a log that’s [notably] decomposing (8) | N |
| SUIT A LOG that’s anagrammed (decomposing) | |||
| 37a | ENDEARS ENDERS |
Makes popular organ with stops on the outside (7) | |
| EAR (organ) with ENDS (stops) surrounding (on the outside) | |||
| 38a | APEPSY | A fizzy drink [Arthur] said gives digestive trouble (6) | A |
| A + PEPSI (fizzy drink), soundalike (said) | |||
| 39a | AEDILE EDILE |
Magistrate I lead astray close to collapse (6) | |
| I LEAD anagrammed (astray) + the last letter of (close to) collapsE | |||
| 40a | SYPES | Local soaks in speakeasy [nattering] peskily (5) | N |
| The answer is in speakeaSY PESkily | |||
| Down | |||
| 1d | AWARD | Grant accepted [Ascot] tie from the south (5) | A |
| A (accepted) + DRAW (tie) upwards (from the south) | |||
| 2d | ERINGOES | Island tries [plucking] thistle-like plants (8) | P |
| ERIN (island) + GOES (tries) | |||
| 3d | DEBONAIR | [Plotter’s] carefree, revolutionary plot being broadcast (8) | P |
| Reversed (revolutionary) BED (plot) + ON AIR (being broadcast) | |||
| 4d | ARAMAIC | Retired spies catching stuff about [rude] language (7) | R |
| Reversed (retired) CIA (spies) taking in (catching) RAM (stuff) and A (about) | |||
| 5d | SPUTNIK | Reversing, family rams [outraged] Soviet traveller (7) | O |
| Reversing, KIN (family) and TUPS (rams) | |||
| 6d | WARFARER | Flipping [pulpy] green food right for hawk (8) | P |
| Backwards (flipping) RAW (green) + FARE (food) + R (right) | |||
| 7d | ALPHABET | Characters in hotel help to support Mountain [Rescue] (8) | R |
| H (hotel) and ABET (help) going under (to support) ALP (mountain) | |||
| 8d | SEGAR SAGER |
Smoke fumes going upwards (5) | |
| RAGES (fumes) going upwards | |||
| 12d | LINDA | Nothing upset [ingenious] lawyer Ms Blair? (5) | I |
| NIL (nothing) reversed (upset) + DA (lawyer) | |||
| 15d | AMBER EMBAR |
Half-cut Yankee pockets black resin (5) | |
| Half-cut AMER[ican] (Yankee) takes in (pockets) B (black) | |||
| 20d | ARRESTEE | Some land filled with wild trees detained [admiring] person in the US (8) | A |
| ARE (some land) filled with an anagram of (wild) TREES | |||
| 22d | CURTSEYS | More than one bob short, [taxpayer] agreed to raise shilling (8) | T |
| CURT (short) + YES (agreed) going upwards (to raise) + S (shilling) | |||
| 25d | UPLAND | In text, you intended to leave north-east [England’s] high ground (6) | E |
| U (in text, you) + PLAN[ne]D (intended) to leave NE (north-east) | |||
| 26d | ELVISH | King Henry [chuntered] made-up lingo (6) | C |
| ELVIS (King) + H (henry) | |||
| 27d | CALLER CELLAR |
Visitor heading for Channel to go across the Channel (6) | |
| The initial letter of (heading for) Channel + ALLER (to go across the Channel) | |||
| 28d | UNEASE | Anxiety of the upper-class seen, a strange [outbreak] (6) | O |
| U ((of the) upper-class) + SEEN, A anagrammed (strange) | |||
| 30d | MESEL | Honey-coated tablets [lessen] bard’s ailment (5) | L |
| MEL (honey)-coated ES (tablets) | |||
| 31d | PETRE | Part of gunpowder tea reportedly drunk by [obstreperous] French father (5) | O |
| T (tea reportedly) inside (drunk by) PÈRE (French father) | |||
| 32d | ATAPS | Palms of Australian [unusually] hot and cold? (5) | U |
| A (Australian) + TAPS (hot and cold?) | |||
| 33d | CAGEY | Secretive, nameless female detective [reappears] on TV (5) | R |
| Without N (nameless) CAG[n]EY (female detective on TV) | |||