Solution to 23D has been deliberately left unsolved and is to be answered only by a non-regular / novice commenter, with proper annotation. Those who have answered earlier in the week, please give others a chance.
Open for anyone to answer, if not solved by 1 PM.
ACROSS
1 Measure of 16, 36 maybe found in carpenter's tool? (6) SQUARE [DD]
5 Cabinet basically worried over a vexatious border (8) WARDROBE {Wo...d}{A}{BORDER*}
9 Surprise from shooter's weapon by enthusiast (4,4) BOWL OVER {BOW}{LOVER}
10 Has two pants? It's not important (2,4) SO WHAT*
11 Hides six-shooter wielding Duke inside for wines (10) BURGUNDIES {BUR{GUN}{D}IES}
12 American jerk (4) YANK [DD]
13 Dissent features in suicide/ murder (5) DEMUR [T]
14 Husband in second air-conditioned train (6) SCHOOL {S}{C{H}OOL}
17 Agree years spent in overseas (3,3) SAY YES {YY} in {SEAS<=}* (Correction - {YY} in {SEAS<=} - See comments)
19 Scottish inventor reportedly consumed drug in cereal (5) WHEAT {(~watt)WHAT}* over {E}
22 Five out of five got 50. It's a record (4) FILE {FIv{L}E}
24 Fly low with courage (10) BLUEBOTTLE {BLUE}{BOTTLE}
26 Associate withdraws support to government bill (8) DIAGNOSE {AID<=}{G}{NOSE}
27 Word play maybe repeater (8) REPARTEE*
28 Man-made hybrid of aster with zinnia mainly (6) ERSATZ {ASTER*}{Zi...a}
DOWN
2 Queen is doubtful about alternative members required for the meeting (6) QUORUM {QU}{UM} over {OR}
3 By all accounts, friend buys story without suspicion in the end (9) ALLEGEDLY {AL{LEGEnD}LY}
4 Malign knight in flat with objectionable material primarily (7) ENVENOM {E{N}VEN}{Ob...e}{Ma...l}
5 He is fussy about Bank of Nile perhaps losing volume (7) WORRIER {ROW<=}{RIvER}
7 Disorderly mob razed college with artillery eventually (5) ROWDY {cROWD}{a...lY}
8 Maybe Einstein goes to bathroom first to take shower before buffet (8) BRAINBOX {Ba...m}{RAIN}{BOX}
15 They have pegs with bowler near stadium seats (3,6) HAT STANDS {HAT}{STANDS}
16 Photoelectric device - An enchanting quality on surveillance (5,3) MAGIC EYE {MAGIC}{EYE}
18 Content with substitute, vacation judge of court (7) SUBJECT {SUB}{JudgE}{CT}
19 Budding forest-fly, I hear (5-2) WOULD-BE (~wood bee)
20 Welcome support cutting short toastmaster (7) EMBRACE {EM{BRA}CEe}
21 Ready to start new Tesla model finally (3,3) ALL SET {TESLA+m..eL}*
23 It goes to in-side and outside (5) E?T?A (Addendum - EXTRA [DD] - See comments)
Reference List
Duke = D, Second = S, Husband = H, Year = Y, Drug = E, 50 = L, Government = G, Queen = QU, Knight = N, Volume = V, College = C, Court = CT, Support = BRA