Solution to 23A 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 solve, if not solved by 1 PM.
ACROSS
1 Two months in the last quarter? Concentrate! (6) DECOCT {DEC}{OCT}
4 Opportunities to head into ship (6) SCAPES {S{CAPE}S}
10 The vile Yemeni, casting malicious look (4,3) EVIL EYE [T]
11 Trained agent putting love behind with rose! (7) TUTORED {T(-o)UT(+o)O}{RED}
12 Ballot for appointment of a military chief? (7,8) GENERAL ELECTION [C&DD]
13 Ordinary, innocuous spice, most ordered! (13) INCONSPICUOUS {INNOCUOUS+SPICe}*
14 You cannot keep sitting on this instruction! (8,5) STANDING ORDER [CD]
21 Played by all fat fans too! It is not a real competition! (7,8) FANTASY FOOTBALL*
22 Give up control over half of Gallic nation (7) REFRAIN {RE{FRAnce}IN}
23 Clues about a forgotten legend of dribble (7) S?I?T?E (Addendum - SPITTLE {TIPS<=}{TaLE} - See comments)
25 See southern parts blast (6) DESCRY {DE{S}CRY}
DOWN
1 Basically to delve, remove earth, dig ground, excavate (6) DREDGE Acrostic &lit
2 Life energy's almost gone anyway, by opening of navel and roll of hair on nape of neck (7) CHIGNON {CHI}{GONe*}{Na..l}
5 Some delicate chunks of resin (7) CATECHU [T]
6 Rest inside Alexander's adversary's territory (7) PURLIEU {PUR{LIE}U}
7 Editor going in without chairs (6) SEDANS {S{ED}ANS}
8 Making fresh arrangement by correcting, taking time out for girl (13) RECLASSIFYING REC(-t+lass)LASSFYING
9 Hero's last manoeuvres involved King's decoy (8-5) STALKING-HORSE {HEROS+LAST}* over {KING}
15 Unfelt, universal, kind of musical (7) TUNEFUL {UNFELT+U}*
16 A raga in flowing river (7) NIAGARA*
17 Rope from Spooner's loo (7) RATLINE (latrine to ratline)
19 Disreputable girlfriend or Church? That's some weight! (6) GFORCE {GF}{OR}{CE} Why disreputable? Enu should be (1-5)
20 Inactive agent has cover (6) SLEEPY {S{LEE}PY}
Reference List
Ship = SS, Southern = S, Time = T, Universal = U, Girlfriend = GF, Church = CE, Cover = LEE