Across:
1 Leaves One Direction for another (CHANGES COURSE) – replacement (CHANGE-) comes ultimately (‘comes’ ultimately = -S) from Journey (COURSE) (CHANGES COURSE),
10 Introduces 2 down (‘ham it up’ = HAM-) to short (n), hard-nosed (‘stern’ without ‘n’ = -STER) (HAMSTER) pet (HAMSTER),
11 Folios (folios = FOOLIS-) produced by (= anagram indicator) second Theatre (second ‘Theatre ‘= -H) (FOOLISH) of the Absurd (FOOLISH),
12 Youngest guys missing (‘youngest’ ‘guys’ missing = onet = NOTE) from The Treasury (bank NOTE),
13 Setting out (= anagram indicator) seats (seats = ASSET) for benefit (ASSET),
15 Characters alongside a nuisance (characters ‘alongside a nuisance’ = DEAN) from college (DEAN),
17 That lady (SHE) at the core of British Empire (at the core of ‘British Empire’ = SHE),
19 Make use of (EMPLOY) foreign (= anagram indicator) mole (mole = EM-LO-) over pressure (-P-) from Yard (-Y) (EMPLOY),
21 Put out (-ISSUE) by first (= positional indicator) Tory leader (‘Tory’ leader = T-) (TISSUE) in The Paper (TISSUE),
22 Claret (RED) to go with lamb (MEAT) (RED MEAT) or steak? (RED MEAT),
23 Those working overseas (FLEETS) providing jobs for those in 7 down (FLEETS providing jobs for ‘sailors’),
25 Turns up (= reversal indicator), fixed charge (fee) is reduced (e) (‘fee’ without ‘e’ = fe = -EF-) in public house (bar = -R-AB) for port (P-) (PREFAB) by one of those accommodating, prepared types off-site (PREFAB),
27 Minor worker (COG) takes the tension out of congestion (takes the ‘tension’ out of ‘congestion’ = cog = COG),
29 The Observer’s (the observers = EYES) content from the Hawkeye State (content from the “Hawkeye State” = EYES),
30 Mass (mass/crowd = SHOAL) for flock? (SHOAL),
31 Content to sponsor a legend (content to ‘sponsor a legend’ = ORAL) in a manner of speaking (ORAL),
34 Change the order (REALIGN) to proper (REAL-) gin (gin = -IGN) cocktail (= anagram indicator) (REALIGN),
35 Alternatively, criticise (LAMBAST /lambaste) the foreign (the = LA-) business graduate (Master of Business Administration = -MBA-) – and that’s just the half of it (‘just’ the half of it = -ST) (LAMBAST),
36 Got into gear? (CHANGED) Figure (PERSON) (CHANGED PERSON), this is what happened when one turned over a new leaf! (CHANGED PERSON).
Down:
2 Overact like Steve McQueen in Bullitt (HAM IT UP) by motorway (MI = -M I-) in Balmoral (Balmoral hat = HA- -T) heading for Ulster (heading for ‘Ulster’ = U-) park (-P) (HAM IT UP),
3 Brazil’s (NUTS) accounts don’t include coca (‘accounts’ don’t include/ without ‘coca’ = unts = NUTS),
4 Serge’s (serges = EGRESS) novel (= anagram indicator) is way out (EGRESS),
5 Firm (CO-) to foot (-F-) the bill from consultant (-FEE) (COFFEE) for stimulant (COFFEE),
6 Half the food (half the ‘food’ = -FO-) in America (US = U-S) (UFOS) produced by crafty types, the subject of conspiracy theorists (UFOS),
7 Man of the cloth (tailor) scratches head (t) (‘tailor’ without ‘t’ = -AILOR-) in boat (S-S) (SAILORS) with all hands on deck (SAILORS),
8 Replace the organ (CHANGE OF HEART) or get a second opinion (CHANGE OF HEART),
9 The copper’s (coppers/small CHANGE-) expertise (ABILITY) (CHANGEABILITY) is compromised by The Amendments (CHANGEABILITY),
14 Fraud (SHAM-) is terrible (poor) – almost (r) (‘poor’ without ‘r’ = -POO) (SHAMPOO) typical of that shower perhaps (SHAMPOO),
16 Types (SORTS) of forecasts that lose face (‘forecasts’ that lose ‘face’ = orsts = SORTS),
18 Man taken out of terminal (“man” taken out of “terminal” = teril = LITRE) has capacity to hold less than two pints (LITRE = 1.75 pints/less than two pints),
20 Most of those (e) in 29 across (‘eyes’ without ‘e’ = YES) could be positive (YES),
21 Fragment of videotaping (fragment of “videotaping” = TAP) from The Wire (TAP),
24 Take a look at (EYE-) liberal (-L-) health and safety authority (Health and Safety Authority = HSA = -ASH) review (= reversal indicator) (EYELASH) by coquettish flutterer (EYELASH),
26 A good way (FAR-) for artist (-RA-) to get green light (-GO) (FARRAGO) in confusion (FARRAGO),
27 Cheating without it? (“cheating” without “it” = cheang = CHANGE) You’ll feel that in the pocket! (CHANGE),
28 What the Arabian might do (Arabian horse might GALLOP) left (-L-) in foreign (= anagram indicator) gaol (gaol = GA-LO-) by political leader? (‘political’ leader = -P) (GALLOP),
32 All the family (KI-N) left (-L-) inside (KILN) for firing those from pottery factory (KILN),
33 Ruler (EMIR) for some theorem irreplaceable (some ‘theorem irreplaceable’ = EMIR).