I have to present the theme answers in pairs to make sense of this. Let's look at the unifier first.
64 A. Intelligence agency employee, and what a black square acts as in rows 3, 5, 8 and 11: CODE BREAKER. A person who solves an encryption code and thus is able to translate and understand messages sent using that code. In the puzzle the names of various types of codes are split, or "broken" by a black square in the grid.
On to the theme fill --
17 A. World's oldest golf tournament: BRITISH OPEN. Founded in 1860, this tournament now rotates among a select group of courses in the U.K.
19 A. __-purpose flour: ALL. There are specific flours for bread, pastry, cakes, and several even more specialized types, like gluten free. ALL purpose flour is a compromise blend made from hard and soft wheat that is good for most purposes.
Spanning the black square we have PENAL. A PENAL code is the collection of laws dealing with crimes and their punishments.
23 A. Course standard: PAR. In golf, the expected number of strokes for a first-class golfer to complete a hole or course.
24 A. Like a big grin: EAR TO EAR. Descriptor for a broad grin on a happy face.
Together they give us AREA. An AREA code is a three digit number that identifies your telephone service region.
39 A. "Name another person": WHO ELSE? Self explanatory
41 A. Some Greek islanders: CRETANS. Inhabitants of CRETE, the largest and most populous of the Greek Islands. It is the 5th largest island n the Mediterranean and 88th largest in the world. Who measures these things?
A SECRET code is a method of encrypting messages to maintain security and confidentiality. This is the sense I was thinking of in the theme title.
52 A. Starbucks amenity: FREE WIFI. A no-fee function granting internet access.
55 A. Short agent?: REP. Abbrv for REPresentative: one who acts on your behalf. Short in the clue suggests an abbreviation in the fill.
A FIRE code is a set of building and property regulations designed to establish a mandatory standard for a building's ability to resist the start and spread of a fire, as well as facilitating the prompt and safe evacuation of the occupants.
Hi gang. JazzBumpa here. Looks like this is the first L.A.T. puzzle by the team of Kevin Christian & Mangesh Mumbaikar Ghogre. Congrats, Guys! Clever and original theme approach and an all-round top-notch puzzle. Now let's break in and see if we can decode it
Across:
1. Out of whack: AMISS. Something isn't right. How come things running smoothly are never in whack?
6. Sounding shocked: AGASP. One of those dreaded A-words you are unlikely to find outside of an X-word.
11. Kissing on a crowded sidewalk, for short: PDA. Public Display of Affection. Regardless of your attitude towards these things, please avoid crowded sidewalks.
14. Dyed fabric: BATIK. An Indonesian technique of wax-resistance dying applied to whole cloth.
15. __ Mesa, Calif.: COSTA. A city in orange Co.
16. Acted as guide: LED. Only if you followed.
20. In itself: AS SUCH. Per se.
21. Short-term sculpture material: ICE. Alas, they melt.
22. Country's Lovett: LYLE. [b 1957] He is an American singer, song writer, actor and producer with 13 albums who has won four grammies. In the early 90s he was briefly married to Julia Roberts. In 2017 he married April Kimble after a 14 year engagement.
26. McKellen of "Vicious": IAN. What - no love for Gandolf?!? He [b 1939] is a versatile British actor.
29. Stout servers: PUBS. Where portly proprietors might also serve you porters.
31. Peddled: SOLD.
32. Febreze target: ODOR.
34. App's early version: BETA. A version made available to a limited group of users for testing.
36. Talus neighbor: TIBIA. The innermost and longer of the two bones between the knee and ankle [talus.]
43. Augment: ADD TO.
44. Vivacity: BRIO.
46. Letter before bravo: ALFA. First letter of the NATO phonetic alphabet, used to spell parts of a message where confusion might occur.
47. Untruths: LIES. Mendacity
49. "Marriage Story" Oscar nominee Driver: ADAM. [b 1983] He has received a Volpi Cup [Venice Film festival] and has been nominated for 3 Academy awards, 2 Emmys and a Tony.
51. Prune: LOP. As, frex. a tree branch.
57. Bonny gal: LASS. A lovely lady from Lanarkshire.
58. Spa bath choice: MUD.
59. Digital brokerage pioneer: E-TRADE. Founded in 1991
63. Angsty music genre: EMO. A variety of pop music similar to punk, but with more complexity and emotion.
66. Monkey in "Aladdin": ABU. Star of the show?
68. Having too much: OD-ING. Figuratively Over-Dosing.
69. Soak (up), as sauce: SOP. As defined - from Old English.
70. See 12-Down: REESE. Delloreese Patricia Early [1931-2017] known professionally as Della Reese, was an American jazz and gospel singer, actress, and ordained minister whose career spanned seven decades.
Down:
1. "Fernando" band: ABBA.
3. Words before and after "what": IT IS. A tautology that developed into an idiomatic phrase indicating the immutable nature of an object or circumstance.
4. Suddenly pay attention: SIT UP. Mental attention reflected in physical posture.
5. Slopes headgear: SKI CAP. Googling gets me knit beanies. Who knew.
6. Berlin cry: ACH. An expression of surprise, impatience, disgust, etc.
7. Most like s'mores: GOOIEST. It's from the toasted marshmallows.
8. Shelter org.: ASPCA. The American Society for the Prevention of Cruelty to Animals, established in 1866.
9. Heads (toward): STEERS. Directs one's direction to.
10. Rave's opposite: PAN. Extremes of the rating spectrum for stage performance. PAN is harshly critical.
11. Cooperated: PLAYED BALL. Worked willingly with others.
12. With 70-Across, "Touched by an Angel" star: DELLA. Vide Supra.
13. Stella __ Studio of Acting: ADLER. [1901- 1992] She was an American actress and acting teacher.[2] She founded the Stella Adler Studio of Acting in New York City in 1949.
18. Bushes: SHRUBS. Woody plants smaller than trees, with several main stems arising at or near the ground.
22. Title girl whose given name is Dolores: LOLITA. Sue Lyon played her in the movie, but could not attend the premier because she was too young
25. Subscriber's bonus: TOTE. Bag for carrying parcels, and frequent promotional gift.
26. Hawkeye State: IOWA. This popular nickname for the state of Iowa is said to have come from the scout, Hawkeye, in James Fenimore Cooper's The Last of the Mohicans published in 1826. According to the Iowa State web site, "Two Iowa promoters from Burlington are believed to have popularized the name." The nickname was given approval by "territorial officials" in 1838, twelve years after the book was published and eight years before Iowa became a state. [Reference]
27. Ritalin target, briefly: ADHD. Attention Deficit Hyperactivity Disorder. A person with ADHD has differences in brain development and brain activity that affect attention, the ability to sit still, and self-control.
28. Ramen restaurant offering: NOODLE SOUP. Ramen are quick cooking egg noodles.
30. U.K. network, with "the": BEEB. The British Broadcasting Corporation.
33. Laces again: RETIES. As shoes.
35. Part of DNA: ACID. The rest is deoxyribonucleic.
37. Recon details: INFO. Information.
38. PDQ: ASAP. Stat. Hurry. Rush. Be hasty.
40. Big name in movie theaters: LOEW. Marcus LOEW [1870 - 1927] was an American business magnate and pioneer in the motion picture industry. He formed the MGM movie studio.
42. Lion, at times: ROARER. Relevant
48. Four-time Olympic gold medal winner Biles: SIMONE. [b 1977] She has a combined total 0f 30 Olympic and World Championship medals, and is considered by many to be the greatest gymnast ever.
Believe it or not I can't do this.
52. Causes of scratching: FLEAS. Small wingless jumping insects that feed on the blood of mammals and birds. They sometimes transmit disease.
53. Recurring Stallone role: RAMBO. Is there always blood?
56. Popular red-carpet fashion: PRADA. An Italian luxury fashion house founded in 1913.
60. Like, with "to": AKIN. Similar
61. 64-Down blemish: DENT. Ouch!
62. Cogito __ sum: ERGO. "I think, therefor I am." Rene Descartes.
64. Garage occupant: CAR. Without blemish, I hope.
65. "Sayonara": BYE. Adios!
Perfect note to end on. Speaking of notes we were also able to get quite a bit of music today.
Happy Wednesday, all. Stay home. Stay safe. Don't break any codes.
Cool regards!
JzB