No real complaints again! There were quite a few combined fodder and action words, which I always think is a bit of a devious trick, especially 21A!

Across

1

How mask is designed for punk styles (7)
MOHAWKS — anagram (designed) of HOW MASK

5

Olympic colours conceal instrument (7)
PICCOLO — hidden in olymPIC COLours

9

Banned keyrings? (5)
TABOO — TAB (key) OO (rings)

10

Gather leaves into swamp in Moroccan city (9)
MARRAKESH — RAKE (gather leaves) inside MARSH (swamp)

11

Refs rant about colour of card handed over (11)
TRANSFERRED — anagram (about) of REFS RANT, RED (colour of card)

12

Just lost foremost voice (3)
AIR — fAIR (just, without first letter)

13

Bird is cautious, following around Sydney players (9)
CASSOWARY — WARY (cautious) after CA (around) SSO (Sydney players; Sydney Symphony Orchestra)

15

Even they meant an African scavenger (5)
HYENA — even letters of tHeY mEaNt An

16

Dense bush not a vehicle to feed parasite (5)
THICK — busH without bus (a vehicle) inside TICK (parasite)

18

Tinned meat complaint following torment (5,4)
BULLY BEEF — BULLY (torment) BEEF (complaint)

20

Prompt express line (3)
CUE — homophone (express) of QUEUE (line)

21

Per transaction, joint collaboration? (11)
PARTNERSHIP — anagram (action) of PER TRANS, HIP (joint)

24

Dom tithes freely to one denomination (9)
METHODIST — anagram (freely) of DOM TITHES

25

Hold baton (5)
STICK — double def.

26

After initial surprise, I'm covered in pastel glitter (7)
SPARKLE — S (first letter of surprise), RK (I'm; the setter) inside PALE (pastel)

27

Son registered and worked hard (7)
SLOGGED — S (son) LOGGED (registered)

Down

1

Turning over the hollow drum for choral piece (5)
MOTET — reversal (turning over) of TE (the without middle letter), TOM (drum)

2

Hubby scratched by key wheel parts (7)
HUBCAPS — HUBby without by, CAPS (key)

3

60s festival from forest to creek's banks (9)
WOODSTOCK — WOODS (forest) TO CK (outside letters of creek)

4

Storms meet oddly at French river (5)
SOMME — odd letters of StOrMs MeEt

5

Depiction of beam in doorway (9)
PORTRAYAL — RAY (beam) inside PORTAL (doorway)

6

Vegetable is cold and firm (5)
CHARD — C (cold) HARD (firm)

7

Excessively indulged lovers later reject boundaries (7)
OVERATE — lOVERs lATEr without outside letters

8

Partner for health/sickness? (5,4)
OTHER HALF — anagram (sickness) of FOR HEALTH

13

Before midday, pet scours burial passages (9)
CATACOMBS — PET (cat) A (middle letter of day) COMBS (scours)

14

Penny leaves new unripe Bega vegetable (9)
AUBERGINE — anagram (new) of UNRIpE BEGA without p (penny)

15

Prose they arrange into magical words (3,6)
HEY PRESTO — anagram (arrange) of PROSE THEY

17

Ate poorly after one month promoting cold drink (4,3)
ICED TEA — I (one) reversal (promoting) of DEC (month), anagram (poorly) of ATE

19

Copying tech, going without leaders (7)
ECHOING — tECH gOING without first letters

21

Cheap wine put down heavily (5)
PLONK — double def.

22

Beginners never outpace the early swimming records (5)
NOTES — first letters of Never Outpace The Early Swimming

23

Prodded to cut short card game - 500 (5)
POKED — POKEr (card game without last letter) D (500)