Solution to 28A 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.
ACROSS
6 The old, old fellow’s line for old British cavalry force (8) YEOMANRY {YE}{O}{MAN}{RY}
10 Starts anchoring a negative news shortly (4) ANON {An...g}{NO}{N}
11 You and I with strict, odd issues to bring in the customs of the US and UK, say (10) WESTERNISE {WE}{STERN}{IsSuEs}
12 Teacher’s back; compete with artist in coastal areas (8) RIVIERAS{SIR<=} over {VIE}{RA}
14 Specify the limits of Davangere ground (6) DEFINE {Da..rE}{FINE}
16 Some took raw vegetable (4) OKRA [T]
19 Sort of knot ship captains may not appreciate (4) REEF [DD]
20 Workers’ leaders about to go — time to agitate (6) FOMENT {FOreMEN}{T}
21 Person with a will to try and toss list back (8) TESTATOR {TEST}{ROTA<=}
24 Nag a pandit to round up wild animal (5,5) GIANT PANDA*
28 Wrong — idol repeats core of a piece of music (5) R?N?O (Addendum - RONDO {wRONg}{iDOl} - See comments)
29 Gandhiji’s anti-engagement policy (8) PACIFISM [CD]
DOWN
1 Free issue about upcoming film (10) EMANCIPATE {EMAN{PIC<=}ATE}
2 Swear numbhead put out reply (6) ANSWER {SWEAR+Numb}*
3 Breads get promotion, we hear (4) RYES (~rise)
4 Welcoming a kind of match teams play (8) FRIENDLY [DD]
5 Managed to hide old colour (4) ROAN {R{O}AN}
7 He, Ann and Lui, all lose first place, because of low interest (5) ENNUI {hE+aNN+lUI}
9 Want sailor to change scene (7) ABSENCE {AB}{SCENE*}
13 Burnt-out writer dumped in street (5) SPENT {S{PEN}T}
15 Workers’ supervisor leaves man dumb on both sides (4,3,3) FORE AND AFT {FOREmAN}{DAFT}
17 More crazy rookie displaced after check at last (7) KOOKIER {ROOKIE}*<=>{c..cK}
18 Fix — accommodate the patient man (3-2,3) PUT-UP JOB {PUT-UP}{JOB}
23 Poor casting includes predators in the main (5) ORCAS [T]
25 RSTVWXYZ? Not acceptable! (3-1) NOT-U Definition by example (Correction NON-U Definition by example - See comments)
26 Brief sleep with English scruff (4) NAPE {NAP}{E}
Reference List
The old = YE, Old = O, Line = RY(Railway), News = N, Artist = RA(Royal Academician), About = RE, Time = T, Over = O, Sailor = AB, Street = ST, Man = M, Som = S, English = E