Across:
8 Tight-lipped (MUT-E) about a (-A-) temperature (-T-) (MUTATE) change (MUTATE),
9 Survives (WEATHERS) work (W-) chopping up (= anagram indicator) ash tree (ash tree = -EATHERS) (WEATHERS),
10 Draw the line without using leather (‘draw the line’ without using ‘leather’ = dwin = WIND) weave (weave = WIND),
11 Broadcast (on = ON) trouble started (‘Trouble’ started = T-) by that man (-HE) voicing (= homophone indicator) disapproval to performers (‘boos’ = ‘BOOZE’) (ON THE BOOZE) in the bar (ON THE BOOZE),
12 Barman (Attorney General = AG-) on holiday (-OUT-) island (-I) (AGOUTI) could be mistaken for a guinea pig (AGOUTI rodent is related to guinea pig),
14 Stops (STATIONS) at the end of 15 across (at the end of ‘weather stations’ = STATIONS),
15 They’re working out which way the wind is blowing (WEATHER STATIONS) for most of those in 9 across (most of those in ‘weathers’ = WEATHER) taking positions? (positions = STATIONS) (WEATHER STATIONS),
18 A (A-) friend from New York (friend/bud = -BU D-) and most of (t) the outfit (habit) (‘habit’ without ‘t’ = -HABI) (ABU DHABI) from sheikhdom (ABU DHABI),
20 Greta Garbo dismissed rota (‘Greta Garbo’ dismissed ‘rota’ = gregab = BEGGAR) for Peter the Tramp, for instance (Peter the Tramp / BEGGAR),
22 Moneylender (PAWNBROKER) on the board (PAWN-) is bankrupt (broke = -BROKE-) and heading for ruin (heading for ‘Ruin’ = -R) (PAWNBROKER),
24 Is lacking compassion (COLD) in backing (= reverse indicator) those in deadlock (those in ‘deaDLOCk’ = dloc = COLD),
25 Fog (M-IST) covering old (-O-), old city (-UR-) on one side of the bridge (one side of the ‘bridgE’ = -E) (MOISTURE) with rising water perhaps (MOISTURE),
26 Rouse (AWAKEN) leading American (‘American’ leading = A-) party for the passing (-WAKE-) of final legislation (final ‘legislatioN’ = -N) (AWAKEN).
Down:
1 Pulling a face (pouting) off the top of one’s head (p) (‘pouting’ without ‘p’ = OUTING) can be exposing (OUTING),
2 Mole from Homeland (‘mole’ from ‘homeland’ = hand = HAND) in full house (full house = HAND in cards),
3 Don’t forget (MEMORISE) viral phenomenon (MEM-E) about old (-O-) teacher (Sir) retiring (= reversal indicator) (Sir = -RIS-) (MEMORISE),
4 Powerful blow (SWAT) found in Washington’s Watergate (found in ‘washingtonS WATergate’ SWAT),
5 A cream (a cream = CAMERA) roll (= anagram indicator) in the hands of the one calling the shots (CAMERA),
6 Giving thought to the idea (THEORISING) The (THE-) Ring (ring = -O-) is revolting (rising = -RISING) (THEORISING),
7 Turns up (= reverse indicator) grandmother (nan = -NAN) from Australia (Oz = -ZO-) joined paramilitaries (IRA = ARI-) (ARIZONAN) – with one of those from the city synonymous with The Rising? (one from Phoenix, Arizona = ARIZONAN),
13 A Mess (a mess = UNTIDINESS) produced by a foreign (a = UN-) order (-TIDINESS) (UNTIDINESS),
14 Part of the Caucasus highlighting (part of the ‘caucaSUS HIghlighting’ = SUSHI) Asian cuisine (SUSHI),
16 Make a big show of (EMBLAZON) direction (East = E-) on Doctor (doctor = -MB-) At Large (-L-) and broadcast (-ON) after (= position indicator) all the letters (‘A to Z’ = -AZ-) (EMBLAZON),
17 Relates to The Joshua Tree (ARBOREAL) identifying with The Big Tree (ARBOREAL),
19 A (A-) town in Meath (Trim = -TRI-M) around unique summit (‘Unique’ summit = -U-) (ATRIUM) that’s close to my heart? (ATRIUM),
21 Teamed up with (ALLIED) yob from Old Bailey (‘yob’ from ‘Old Bailey’ = ldaile = ALLIED),
23 Some upset (= reverse indicator) escapee kidnapped (some ‘escaPEE Kidnapped’ = peek = KEEP) from castle (castle = KEEP),
24 Reeks from mackerels (‘reeks’ from ‘mackerels’ = macl = CLAM) in chowder (CLAM).