The preamble seemed quite straightforward, no extra letters etc in the wordplay just the possible modification of six across answers and twelve down ones before entering them in the grid.
I started with the down clues and it quickly became clear that some of the answers were too long for the space available in the grid and some too short, always by one letter. After solving a few of the first across clues it appeared that one letter in some of the down clues was being duplicated before entry.
At this stage I had a possible DO??????????? for the unclued 21ac and, given the enumeration, I took a guess at DOUBLE OR QUITS which would fit in with the title and with duplicating or removing a letter. It turned out that my guess was correct because two of the thematic across clues were soon solved and these could only be entered by the removal of two occurrences of ‘or’.
So, ‘double or’ quits six of the across clues, a letter in six down clues is repeated (‘doubled’) and a letter is removed from (‘quits’) a further six down clues. The repeated letters and the removed letters in the down clues could both be rearranged to give GAMBLE which was to be written below the grid.
My lucky guess meant that this puzzle didn’t prove to be particularly difficult. In fact it was probably my quickest EV solve for several months but this didn’t detract from the enjoyment.
*(XXX) – anagram
[x] – letter(s) unused
X – duplicated letter
x – removed letter
Across
1 C[or]OC[or]O R (run) in COO (expression of surprise) repeated
4 STATS TAT (rubbish) in SS (found on board)
8 S[or][or]IAL SOR[t] (mostly kind) I (one) in ORAL (exam)
11 IRON ORE R (run) ON OR (gold) in IE (that is)
13 TATOU T[ail] O (of) in TAU (cross)
14 SAMEL *([f]LAMES)
15 MIN[or] [or]DERS *(DONE MIRRORS)
16 CAMELEON CAMEL (desert animal) *(ONE)
17 DRAT TAR (sailor) ‘D (had) reversed
19 NICE N[ature] ICE (reserve)
21 DOUBLE OR QUITS unclued
23 KETA hidden in ‘caKE TAinted’
27 GYRE *(GRE[ed]Y)
28 OUTREACH OU (university) R (Rector) in TEACH (educate)
29 GROWN-UP W (women) N (new) in GROUP (collection of people)
31 M[or]ASS [or]E MORAS (delays) SORE (sensitive)
32 HONEY hidden in ‘nourisH ONE Yes’
33 FRETSAW FR (frequently) WASTE (rejected) reversed
34 T[or]EAD[or] READ (learned) in ROOT (cheer) reversed
35 ANGST ANGST[rom] (Swedish physicist losing memory)
36 M[or]AT[or]Y MORA (game) TORY (right-winger)
Down
1 CISCO hidden in ‘atlantiC IS COnsidered’
2 ORAATORY ORA[l] (most of spoken) [s]TORY (tale dismissing first)
3 COMMP CO (company) MP (moderately soft)
4 SOLLE SOL[ac]E (pleasure having disposed of bill)
5 TRIENEE TRIE (historic attempt) NE (not once)
6 THINg *(NIGHT)
7 STaNCE ANC (African party) in STE[w] (difficulty ignoring Western)
8 SAD dd
9 bITERS BIT (a little) ER[o]S (love, nothing less)
10 LUSTReS LUST (desire) RES[t] (most of others)
12 NEEDBBE NEE (born) *(BED)
17 DRUmBEAT [wa]R in DUMB (lost for words) EAT (worry)
18 ATTIC SAlT ATTIC (story) SALT (sailor)
20 CRATERS [inswinge]R in CATERS (fours, not any more)
21 DIGGHT DIG (approve) H[ungarian] T[rade]
22 TRONA AN (one) ORT (left-over portion) reversed
23 KENYA N (North) in KEY (of great importance) A (America)
24 ARMET [w]AR (head lost in conflict) MET (satisfied)
25 LASSA ASSA[i]L (attack doing for one) reversed
26 CHEWY CH (church) *(YEW)
28 OURN O (circular feature) URN (vase)
30 WED dd