Solution to 25A 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 Use sexier moves to enthrall college sweetheart (8) EXERCISE {EXER{C}IS*}{swEet}
5 Ignores urges to consume heroin finally (6) SPURNS {SPUR{h...iN}S}
10 Deception to get hold of complete genetic sequence (5) CODON {CO{DO}N}
11 Centre ordered — maintain distance, showing restraint (9) RETICENCE {RET{ICE}NCE*}
12 Force returns to investigate about trouble in European city (9) MARSEILLE {RAM<=}{SE{ILL}E}
13 Posh woman in retro joint is not married (5) UNWED {U}{DE{W}N<=}
15 Frank in South African province, going round ancient city (7) NATURAL{NAT{UR}AL}
18 Stories of stars acting out after consuming dope (7) LEGENDS {LEa{GEN}DS}
20 Somehow stayed sober (6) STEADY*
24 Bill steals fancy earring, gets indicted (9) ARRAIGNED {A{EARRING*}D}
25 Bomb went off outside court — ultimately shocked (9) A?T?U?D?D (Addendum - ASTOUNDED {A}{S{c..rT}OUNDED} - See comments)
26 Creep with cold sore on left side of lip (5) CRAWL {C}{RAW}{Lip}
27 Score with woman enthralled by wine at end of party (6) TWENTY {T{W}ENT}{p..tY}
28 Confined goon smuggling kit with ecstasy (8) CLOSETED {CLO{SET}{E}D}
DOWN
1 Some green campaigners settle in tents (6) ENCAMP [T]
2 Authorising to stop endless revelry involving immorality (9) ENDORSING {END}{OR{SIN}Gy}
3 Get in and naughtily discuss about grown-up who’s willing to have sex (10,5) CONSENTING ADULT {CONS{GET+IN+AND}*ULT}
4 Stumped by twists and turns (7) STROLLS {ST}{ROLLS}
6 Recover from shock and take care of shattered glass (4,2,3,6) PICK UP THE PIECES [DD]
7 Rejuvenate in serene woods (5) RENEW [T]
8 Scheming to trap mysterious revolutionary on island quickly (8) SPEEDILY {S{DEEP<=}{I}LY}
9 Newts swimming across river dispersed (6) STREWN {ST{R}EWN*}
16 Sacked revolting director, stark-naked in rave (9) REDUNDANT {D}{NUDE}<= in {RANT}
20 Rustled up a pastry (7) STRUDEL*
23 Learn about bug’s short bristles (5) SETAE {SE{TAp}E}
Reference List
College = C, Posh = U, Woman = W, Acting = A, America = A, Bill = AD, Cold = C, Wine = TENT, Ecstasy = E, Stumped = ST, Island = I, River = R, Director = D, Power = P