Across:
1 In awe of (AMAZED) an open (‘an’ open = A-), old prison (-MAZE-) for five hundred (Roman 500 = -D) (AMAZED),
4 First (A-) sign (-V- sign) in Charleston (dance = -D-ANCE-) school (-S) (ADVANCES) of approaches (ADVANCES),
9 Of course (ENTREE), this should get the juices flowing! (ENTREE),
10 Criminal (= anagram indicator) blamed me (blamed me = EMBALMED) pumped with drugs just like Mummy (EMBALMED),
12 Sweeping (BROAD) existing (‘being’ = ‘BEAN’) report (= homophone indicator) (BROAD BEAN) produced by Pulse (pulse = BROAD BEAN),
13 Sounds like (= homophone indicator) something you’d get from the bank (‘a loan’ = ‘ALONE’) without help (ALONE),
14 Look the other way (TAKE NO NOTICE) leading to bypass (bypass/avoid = TAKE NO NOTICE),
18 Post worker (worker at ‘The Post’ = NEWSPAPERMAN) runs daily (NEWSPAPERMAN),
21 Jelly (ASPIC) Babies to finish (‘babies’ to finish = -S-) after (= positional indicator) a (A-) short film (-PIC) (ASPIC),
22 Allotment (ALLOWANCE) permit (ALLOW-) for area (-A-) near back garden (back/rear ‘garden’ = -N-) and church (Church of England = -CE) (ALLOWANCE),
24 Lay down (KEEP-) type of wine (-SAKE rice wine) (KEEPSAKE) for the memorial (KEEPSAKE),
25 Some upstart is troublesome (some ‘upstART IS Troublesome’ = ARTIST) and responsible for 2 down (ARTIST is responsible for ‘artworks’),
26 Part payments for (DEPOSITS) butcher’s (= anagram indicator) topsides (topsides = DEPOSITS),
27 Put on (STAGED) Degas (Degas = S-AGED) retrospective (= reversal indicator) over time (-T-) (STAGED).
Down:
1 Travelling (= anagram indicator) by air, etc., (by air etc = ACERBITY) out of bitterness, in a manner of speaking (ACERBITY),
2 Star- (star = ART-S) -struck (= anagram indicator) securing job (-WORK-) (ARTWORKS) in The Louvre (ARTWORKS),
3 Characters in The Wise Men deceived (some of ‘the wisE MEN Deceived’ = EMEND) by Polish (polish/revise = EMEND),
5 It’s beyond doubt (DEMONSTRABLE) brute (DEMON-) gets head right (head ‘right’ = -R-) in Arabian accommodation (Arabian/horse accommodation = -ST-ABLE) (DEMONSTRABLE),
6 Goes around (= reversal indicator) volcanic rock (lava = AVAL-) and (and) most of (d) (“and” without “d” = -AN-) the revolutionary (-CHE) (AVALANCHE) deluge of snow (AVALANCHE),
7 State (= homophone indicator) regime change (‘coup’ = ‘coo’ = CO-O-) involves Frenchmen (Messieurs = -MM-) and new (-N) (COMMON) general (COMMON),
8 Trade discount doesn’t include ricotta (‘trade discount’ doesn’t include ‘ricotta’ = dedsun = SUDDEN) or what comes out of the Blue (SUDDEN),
11 Thuggish leader (‘thuggish’ leader = T-) in Clare (-ENNIS) linked to shady business (RACKET) (TENNIS RACKET) is subject of underhand tactics in court (TENNIS RACKET),
15 Can’t complain about that (NO EXCUSES) negative response (NO) to why it went wrong (EXCUSES) (NO EXCUSES),
16 Correcting (EMENDING) engineer (E-) putting things right (-MENDING) (EMENDING),
17 A foreign (a = UN-) paper (-TEST-) journalist (-ED) (UNTESTED) has not been through the hoops (UNTESTED),
19 Made an impression on (MARKED) writer (marker) briefly (r) (‘marker’ without ‘r’ = MARKE-) with director (-D) (MARKED),
20 Maintenance (UPKEEP) of university (U-) creates pressure (-P-) on store (store/save = -KEEP) (UPKEEP),
23 Sort (sort = -ORST) out (= anagram indicator) after (= positional indicator) win (W-) (WORST) that’s least satisfactory (WORST).