4081 Double Cross by Radix

Radix gave us what was really two crosswords. The elegant double clues gave answers that completed two different grids. The solver was left with the decision as to which grid had the correct answers. The cautionary message given by the rogue letters, either added or omitted, gave YOU MAY NEED TO CONSIDER THE OTHER CLUES INSTEAD. There was a hidden message creating a diagonal cross in each grid. These were THESE ANSWERS SHOULD BE USED and PLEASE IGNORE THESE ANSWERS. This was a straightforward instruction as to which grid to submit  and which message to write below the grid.

Rogue letters are shown in [ ].

Across
1 Yo, Scot after punishment, repeated punishment, strode back virtually decapitated, cut in half (5)
TOCOS Anagram [Y]OSCOT; PACED DECAP(itated) reversed
5 Board's to look after university grandee endlessly suffering external eye defects, also suffering with internal defect (7)
ENGUARD (B[O]ARD’s) Anagram U + GRADE(e); ALBUGOS BUG in Anagram ALSO
10 "Hello Sailor!" - Captain RN in variety entertainment (4)
AHAB AH + AB (Ref. Captain Ahab); OLLA ([U]RN) 2 definitions see OLIO
11 Grass in sack returned before prisoner's run in - one conditionally released a part within confines of Pentonville (7)
PILCORN LIP (S[M]ACK) reversed + R (run) in CON; PAROLEE A ROLE in P(entonvill)E
12 Part of vault that is empty ruin with the Parisian ringing, ringing - stem Quasimodo finally (6)
LIERNE IE (that is) + R(ui)N in LE; REECHO REECH (ste[A]m) + (quasimod)O
13 Dyes are red and green - what chippy may need is about 400 in red or green (6)
RESEDA Anagram D[Y]ES ARE; RIPSAW RAW containing P (400) in IS
15 What may appear in bloom in Algeria by middle of May, long due, though, after two quarters (4)
ALGA ALG + (m)A(y); SEIF (long du[N]e) S + E + IF
16 Opening presents from Henry - sendals, fizzy wine - ensure tea is brewing (8)
HANDSELS H (Henry) + Anagram SENDALS: SAUTERNE Anagram ENSURE T[E]A
18 Do central quartet of canaries - serin, maybe - perhaps troll, eg, or trill? (4)
RAIN (SERIN[E]) Anagram (ca)NARI(es); OGRE Anagram EG OR
20 Old farmer protecting very, very heavy style of boots would not once tramp home - after wheedling! (6)
BOVVER VV in BOER; NILLED DELL IN reversed (after whee[D]ling)
23 St Swithin, viz start of rain by God, trashing indoors? House has almost nothing after flood (6)
SIERRA (S[T]) S Swithin less WITHIN (indoors) + IE (viz) + R(ain) + RA; SEANAD SEA (flood) + NAD[A]
25 Covered $100 by bank, British one (in Edinburgh?) (4)
CLAD C + LAD (B[O]Y); BRAE BR + AE
26 Earthy spirit of loco digester - loco needs senna, some might say, as a laxative (8)
ERDGEIST Anagram DIGESTER; LOOSENER LO[C]O + SENER Homophone SENNA
28 Class one hundred and fifty one - bat won after seventy, century and duck (4)
CLAN CL (150) + AN; SCOW (bo[A]t) S (70) + C (century) + O + W (won)
31 Fiddler will see company minstrels in second company dance (6)
ENESCO Anagram SEE[N] + CO; SCOPAS S + CO + PAS
32 Half-hearted assassin finally displaying some energy requires one J, jumping on the spot (6)
KILERG KIL(l)ER + (displayin)G; ENJOIN (require[S]) Anagram ONE J + IN
33 Scene of operations that were initially cancelled, altering special spaces for old lungs, maybe (7)
THEATRE Anagram THAT (w)ERE; SHASHES S (special) + HASHES (ling[I]s)
34 Queen heard about northern beef market (4)
HERA Anagram HEAR[D]; MART  definitions
35 Some stars present Mobil Pacific money, returning bauble for island monument (7)
SERPENT Anagram (mobil[E]) PRESENT; TALAYOT TALA + TOY reversed
36 Unprofitable ruse once used to be English dogs bred to fight against commando regiment (5)
WASTE (unprofitable [R]use) WAST + E; TOSAS TO + SAS
 
Down
1 One in Rio harbour stops, salutes sloppily and pitches quaintly (7)
PORTHOS (ONE in [T]rio) PORT + HOS; TALUSES Anagram SALUTES
2 Cries of emotion as state sheltered, in midst of gale, sheep (4)
OHIO 2 definitions OH + IO; ALEE central letters gALe s[H]EEp
3 Pause after breakdown, rescue not completed, AA shower possibly quit London area (7)
CAESURA Anagram RESCU(e) + AA; CLEANSE CLEAN (quit[E]) + SE (of England)
4 Sensible nurse when raised pulse held up on Loire (4)
SANE EN + AS reversed; DAHL HAD reversed + L (L[O]ire)
5 It turned up in clown's finale, a spider - that clown reacts with ire (6)
APOGEE EGO (I[T] reversed in APE; EPEIRA Anagram APE + IRE
6 Black Rhodesian writer wishing happiness to ashen, good and ill, African men (8)
BLESSING B + LESSING; GRISEOUS G (good) + RISE ([H]ILL) + OUS
7 Concord maybe confused Gore - Gore's old, plus! (4)
GOER Anagram GORE (Concord[E]); ALSO AL’S (ref. Al Gore) + O (old)
8 Prepares crash, given command: Chindit leader's given name to radical (7)
READIES 2 definitions C[R]ASH; ORDERED ORDE + RED
9 Wretch has nearly uncovered crime on (ex) minister (5)
14 Pay Jack to contend with puffed up Hutton after "bottoms up!" (7)
PURVIEW (p[L]ay) PUR (Jack) + VIE + W (with); SWOLLEN LOWS reversed + LEN (ref. Cricketer Len Hutton)
15 To sum up, char's last to join us to get to grips with dustpan, working in earnest (7)
ADDRESS ADD + (cha)R+ ESS ([U]S); STAND-UP Anagram DUSTPAN
17 Rat in a state in washing liquid that is grimy, squealing? (8)
EVALUATE (rat[E]) VA (Virginia) in ELUATE; SCREECHY SC (that is) + REECHY
19 Fish: to split up one at beginning of holiday, a ray indeed, is, for Will in the country, de-stressing (7)
PIRANHA RIP reversed + AN + H(oliday) A; RELÂCHE RE (ray) + LA (indeed) + CHE (I[S])
21 Birds in post office after foreign currency, while customers consider returning after 5 am (7)
LEIPOAS LEI + PO + AS (while); VENDEES V (5) + END (a[I]m) + SEE reversed
22 Hen, for instance, with head in sand? The reverse! End with tête up, reducing strain (7, two words; 7)
RARE GAS  AREG (sand) in RAS (He[N], helium); DETENTE Anagram END + TETE
24 Calorie in salad of token light lunch - most lack lunch's starter - that is binding (6)
NOCKET C in Anagram TOKEN; IDLEST (most [S]lack) L(unch) in ID EST (that is)
25 Confounded bishop, in order to avoid Inge's society, squints (5)
BLEST B + LEST; CASTS CAST ([T]inge) + S (society)
27 Dead calf left after first half of month - female animal finally bore healthy one on NZ farm (4)
VEAL VEA(dar) + L; DOER DOE + (bo)R[E]
29 Smear from dramatist into smashing bias among inhumane whites (4)
OINT Anagram INTO; ANEW (bi[A]S Hidden
30 Ross rule among Scots to block their worthless content of sporrans (4)
DIRT [D]ross R in DIT; ORRA Hidden