Across:
1 Arrangement (FORMAT) to get relative (-MA-) trapped in castle (FOR-T) (FORMAT),
4 Chopped (= anagram indicator) cedars (cedars = -SED CAR-) in America (U- -S) (USED CARS) sold in lots in New York (USED CARS sold in car lots in New York),
9 Travelling (= anagram indicator) horde (horde = RED HO-) taking car (model -T) (RED HOT) that’s smoking? (RED HOT),
10 They’re providing security (WATCHMEN) for Louis-François Cartier and Rolex’s Hans Wilsdorf perhaps (Louis-François Cartier and Rolex’s Hans Wilsdorf: examples of watch manufacturers/watchmen = WATCHMEN),
12 Turns up (= reverse indicator), single (-I) tweeter (-TIT-) without limits (without ‘r’ + ‘s’) refers (‘refers’ without ‘r’ + ‘s’ = EFER) to new (N-) (NEFERTITI) and old Queen (Egyptian Queen NEFERTITI),
13 Lament (DIRGE) preachings from graphic designer (‘preachings’ from ‘graphic designer’ = gdier = DIRGE),
14 Make sure it doesn’t hit the skull (MIND YOUR HEAD) of duck (MIND YOUR HEAD),
18 Player (ACTOR) shooting (BUDDING) opener (= positional indicator) (BUDDING ACTOR) is expected to play a part in the future (BUDDING ACTOR),
21 Slice of freedom – a hallmark (slice of ‘freedom – a hallmark’ = OMAHA) of a part of Nebraska (OMAHA),
22 Won’t get anywhere fast (SLOW TO ACT) cautiously playing part in Long Day’s Journey into Night presumably (SLOW TO ACT),
24 Comet (Comet = Santa’s REINDEER) seen in the sky once a year? (REINDEER),
25 Ombudsman dismisses bad (‘Ombudsman’ dismisses ‘bad’ = omusma = SUMMON) call (SUMMON),
26 Course (ROAD) study (TEST) (ROAD TEST) is an indication of how the coach is working (ROAD TEST),
27 Side-tracks (SHUNTS) search (-HUNT-) in boat (S-S) (SHUNTS).
Down:
1 Fair amount of (half of) 1 across (half of ‘format’ = FOR-) getting mail (-E- mail) from celebrity (-NAME) (FORENAME) – it could be Peter, Paul or Mary? (FORENAME),
2 Dramatically change (REDEFINE) type of wine (RED- wine) from the bottom of France (bottom of ‘France’ = -E-) – the type the oenophiles would appreciate as superior (-FINE wine) (REDEFINE),
3 The secret affair (AMOUR) of removing pets from mousetrap (removing ‘pets’ from ‘mousetrap’ = moura = AMOUR),
5 In a manner of speaking (SPANISH), initial interruption (initial ‘interruption’ = -I-) in two broadcasts (on + on = ON-ON) (SPANISH ONION) is a product of Basque plot (SPANISH ONION),
6 It’s a real theatrical offering from the box (DOCUDRAMA) serving up (= reversal indicator) cod (cod = DOC-) starter unique (starter ‘unique’ = -U-) to happy days (Beckett’s Happy Days = -DRAMA) (DOCUDRAMA),
7 How can you think highly of (ADMIRE) a (A-) department (-D-) that’s bog standard? (-MIRE) (ADMIRE),
8 Blow the whistle on someone locally (SING-) in hospital (-ER) (SINGER) working in theatre (SINGER),
11 What can be quickly converted into cash (LIQUID ASSETS) from Irish Water’s balance sheet presumably (LIQUID ASSETS),
15 I completely agree (YOU SAID IT) yob (yob) briefly (b) (‘yob’ without ‘b’ = YO-) goes to America (USA = -U SA-) to one (-I-) college (Dublin Institute of Technology = DIT = -D IT) (YOU SAID IT),
16 Brainless type (STRAW MAN has no brain in The Wizard of Oz) reviews (= reversal indicator) cultural pursuits (arts = STRA-) at work (-W) with staff (MAN) (STRAW MAN),
17 Reports (WRITINGS) of woman (W-) from Rising (rising = RI-INGS) organising (= anagram indicator) around square (-T- square) (WRITINGS),
19 Little devil (HORROR) from The Bride of Frankenstein, for example (Bride of Frankenstein = HORROR film),
20 Criminal (= anagram indicator) avails (avails = SALIVA) of what mouthy type produces (SALIVA),
23 It can be hard (TOUGH) for enemies leaving meeting house (‘enemies’ leaving ‘meeting house’ = tghou = TOUGH).