Solution to 9A 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
1 John returned home drunk (6) CANNED {CAN}{DEN<=}
4 I don't know what the passenger in a hurry might have told airport security (6,2) SEARCH ME [DD]
9 Translation of “Happy Prince” getting scrapped by master, possibly? (6) M?Y?A? (Addendum - MAYHAP {HA(-p+ma)MAY}* - See comments)
10 Topical article backing a mass movement (8) THEMATIC {THE}{A+M<=}{TIC}
11 Lively interiors of Nice inspired poet's first published work (6,8) EDITIO PRINCEPS {nICe+INSPIRED+POET}*
13 Revolutionary youth checks quiz with a clue about seminal work on socialism (3,7) DAS KAPITAL {LAD<=} over {ASK}{A}{TIP<=}
14 Like some proof I safely turned over (2,2) AS IF [T<=]
16 Women, chiefly from old Ottoman sultans' courts (4) WOOS {W}{Old}{Ot...s}{Su...s}
18 Creep hired busy code-breaker (10) DECIPHERER*
21 Study of heat flow in “Applied Chemistry and Elements of Organic Microanalysis” (14) THERMODYNAMICS {CHEMISTRY+AND+Or...c+Mi...s}*
23 Ordinary soft drinks these days exhibit a milky iridescence (8) OPALESCE {O}{P}{ALES}{CE}
24 Fellows trespassing close to the milk shed (6) EFFUSE {thE}{FF}{USE}
25 Endless test? (4,4) TAME DRAW [CD]
26 Charge on beer bottles (6) ALLEGE {AL{LEG}E}
DOWN
1 Avtaar's about to visit church for a shoot (4) CYME {C{MY<=}E}
2 A Democrat caught between negative and positive responses for executions by drowning (7) NOYADES {NO}{Y{A}{D}ES}
3 English artist joins maverick saint who believes the state should control religion (8) ERASTIAN {E}{RA}{SAINT*}
5 Urge husband to replace pictures at the entrance while transportation to another country (11) EXHORTATION EX(-p+h)HORTATION
6 Land in vacated ranches for European city residents (6) ROMANS {Ran{OMAN}cheS}
7 About to leave game for a short time? At the end, press Alt+F4 and Ctrl-Alt-Del, maybe? (3,4) HOT KEYS {HO(-c+t)TKEY}{p..sS}
8 A poor example of former pro getting wrong cues (6,3) EXCUSE FOR {EX}{CUES*}{FOR}
13 Keep away from party by West Indian dealer outside hotel (2,7) DO WITHOUT {DO}{WI}{T{H}OUT}
15 Spurious fuel supply? Outrageous! (8) SHAMEFUL {SHAM}{FUEL*}
17 Scratching backside, move rear around with upper limb going across the shoulder (7) OVERARM {MOVe+REAR}*
19 Retiring on what I compose for the audience (7) RECLUSE {RE}{CLUSE(~clues)}
20 Commencement of indispensable repair jams power loom (6) IMPEND {In...e}{M{P}END}
22 Entertain female mentees every now and then (4) FETE {F}{mEnTeEs}
Reference List
John = CAN, Mass = M, Women = W, Ordinary = O, Soft = P, These days = CE, Fellow = F, On = LEG, Church = CE, Democrat = D, English = E, Artist = RA, Husband = H, About = C, Over = O, Court = CT, Party = DO, Hotel = H, On = RE, Power = P, Female = F