Times 28,223: Cored Almighty

My favourite thing was probably CASH LAND, cancelling out some of the emotional trauma caused by the supposed homophone at 22dn. Thanks setter!

Definitions underlined, (ABC)* indicating anagram of ABC, {} deletions and [] other indicators.

Across
1 Piece of music has magnificent opening (5)
CHASM – hidden in {musi}C HAS M{agnificent}
4 Vitamin primarily alleviating discomfort if colic’s bad (5,4)
FOLIC ACID – (A{lleviating} D{iscomfort} IF COLIC*)
9 Diligent help almost keeping couple united (9)
ASSIDUOUS – ASSIS{t}, “keeping” DUO
10 One on flight to watch carefully, we’re told (5)
STAIR – homophone of STARE
11 No Yankee reactionary has Socialist backing over there (6)
YONDER – reversed NO Y + reversed RED
12 Enriched fruit drink, sophisticated sort (8)
SMOOTHIE – double def
14 Frantic partners put on odd bits of dress (10)
DESPAIRING – PAIRING put on D{r}E{s}S
16 Retro science facility, source of medicinal lotion (4)
BALM – reversed LAB + M{edicinal}
19 Marketeer‘s minimal stock purchased in Vienna (4)
SPIV – S{tock} P{urchased} I{n} V{ienna}
20 Changed side for Lord’s is fully updated (8,2)
SWITCHED ON – SWITCHED [changed] + ON [side, in cricket]
22 Dispatch book left behind by somebody (8)
CELERITY – CELE{b}RITY
23 Bear to the left, reaching city’s stall at fair (6)
HOOPLA – reversed POOH + L.A.
26 Defective weight or, conversely, any number of grams (5)
WRONG – W(eight) + reversed OR + N G(rams)
27 Mum forming part of twosome getting spliced at sea? (4,5)
MAIN BRACE – MA IN BRACE
28 Freshly brewed tea missed cup (9)
DEMITASSE – (TEA MISSED*)
29 Theologist invested in home improvements very little (5)
DIDDY – D.D. “invested” in D.I.Y.
Down
1 Big Eddy‘s circumspect bids scuppered (9)
CHARYBDIS – CHARY [circumspect] + (BIDS*)
2 Child follows retreating gunners, firing irregularly (5)
ARSON – SON follows reversed R.A. “Firing” as in “setting fire to”, “irregularly” as in “illegally”
3 Gothic gong I’ve improperly seized (8)
MEDIEVAL – MEDAL, “seizing” (I’VE*)
4 Small section of verse also fine on reflection (4)
FOOT – reversed TOO F
5 Take time to record final? (4-6)
LAST-MINUTE – LAST [take time, as in “it lasted 4 hours”] + MINUTE [to record]
6 Court order restricting American patronage (6)
CUSTOM – CT O.M. “restricting” U.S.
7 Runs into region where there’s money maybe for pancake? (5-4)
CRASH-LAND – R “into” CASH LAND
8 Woeful setting for grand part of requiem (5)
DIRGE – G “set in” DIRE
13 Conclude activity on field to lure foxes (4,6)
DRAW STUMPS – DRAW [to lure] + STUMPS [foxes]
15 Large pantry not yet full? (9)
STILLROOM – if it’s not yet full, there’s STILL ROOM
17 Unnamed lady cleared out ground in routine manner (9)
MUNDANELY – (UNNAMED L{ad}Y*)
18 Beaten cricket coach ultimately cheated (8)
THROBBED – {cricke}T {coac}H + ROBBED
21 Promising biographer’s first title (6)
BRIGHT – B{iographer} + RIGHT [title]
22 Cried like a corvid deprived of heart, so we hear (5)
CAWED – homophone of CORED, allegedly
24 Material lodged underneath piano (5)
PLAID – LAID underneath P
25 Increase in price for walking tour (4)
HIKE – double def