Across:
8 Part of the theorem overcompensates (part of the ‘theorem overcompensates’ = REMOVE) to take off (REMOVE),
9 Spud’s (POTATOES) offering the makings of more than one of those in 24 across (POTATOES = the making of more than one ‘chip’),
10 What do you make of 9 across (you can make MASH out of ‘potatoes’) in Crush? (MASH),
11 Soul mate (BODY and soul) writing (from the 3Rs = -R-) in French romance (French ‘romance’ = amour = A-MOUR) (BODY ARMOUR) produces cover up that’s useful to those in 18 across (BODY ARMOUR is useful cover-up to those in ‘barracks’),
12 Assistance sought (HELP-) in hospital (-ER) (HELPER) for right-hand man (HELPER),
14 Group of shops (CH-AIN) around a (-A-) place (-PL-) (CHAPLAIN) keeping the faith in the units (army CHAPLAIN),
15 Caused some damage (CHIPPED) to 9 across? (‘potatoes’ = POTATOES) (CHIPPED POTATOES) They’re found in 25 across! (CHIPPED POTATOES found in ‘chip shop’),
18 Pub (BAR-) set up by sommelier in The Cellar (-RACKS) (BARRACKS) in private quarters (private quarters/ army private quarters = BARRACKS),
20 Temporary occupant (LESSEE) of port (port/left = L-) city in Germany (Essen) hasn’t finished (n) (‘Essen’ without ‘n’ = -ESSE-) engineering (-E) (LESSEE),
22 Follow (TAIL-) those on the board (-PIECES on chess board) (TAILPIECES) for the final parts of the stories (TAILPIECES),
24 Note (music note C-) in Vogue (-HIP) (CHIP) held by gambler (CHIP),
25 Take away (takeaway = CHIP SHOP) 24 across (‘chip’ = CHIP) from small (S-) dance (-HOP) (CHIP SHOP),
26 Old (O-) writer (-PEN-) has only (only) a fair amount (half of) (half of ‘only’ = -LY) (OPENLY) for all to see (OPENLY).
Down:
1 Teased (teased = SEDATE) criminal (= anagram indicator) with dope (SEDATE),
2 Moving back and forth doing the rounds (‘moving back and forth’ doing the rounds = MOTH) can be a pest (MOTH),
3 Beers on a (beers on a = SEABORNE) craft (= anagram indicator) carried by the waves (SEABORNE),
4 A slice of Christmas pudding (a slice of ‘Christmas pudding’ = SPUD) is similar to one of those in the end of 15 across (SPUD similar to one ‘chipped potato’),
5 Set up (= reversal indicator) to (to = OT-) start trouble (start ‘trouble’ = -T-) for a (-A-) short (r) war (‘war’ without ‘r’ = -WA) (OTTAWA) in North America (OTTAWA Canada),
6 Ultimate (ultimate = -TIMULATE-) play (= anagram indicator) set in ship (S-S) (STIMULATES) excites (STIMULATES),
7 Place (-PUT-) in Waterford (The Déise = DE-ISE) (DEPUTISE) for delegate (DEPUTISE),
13 Sounds like (= homophone indicator) Daly (“daly” = “daily” = PAPER) has television excerpts (CLIPS) (PAPER CLIPS) of those holding things together in The Office (PAPER CLIPS),
14 Wraps (CAPES) 23 down (‘cape’ = CAPE-) for final programmes (final ‘programmes’ = -S) (CAPES),
16 Part of the body (HEAD-) with a (-A-) revolutionary (-CHE) (HEADACHE) pain at the top (HEADACHE),
17 Discuss the job (TALK SHOP) of removing leader (s) of the hunt (‘stalk’ without ‘s’ = TALK) and a fair amount (half of) of 25 across (half of “chip shop” = SHOP) (TALK SHOP),
19 An old chestnut (CLICHé) – Sam is off the chemicals (‘Sam’ is off the ‘chemicals’ = cheicl = CLICHé),
21 If Baudelaire loses aura (‘Baudelaire’ loses ‘aura’ = bdelie = EDIBLE) it will go down well (EDIBLE),
23 Stole (stole/shawl = CAPE) loan from Al Capone (‘loan’ from ‘Al Capone’ = acep = CAPE),
24 Meditate over (CHEW over) fragment of Nietzsche wisdom (fragment of ‘Nietzsche wisdom’ = CHEW).