After filling the grid solvers must change the two entries in one row to form the first in a series in full, thereby changing four down entries into followers in part. Seven other entries must be changed into followers in the series. The circled cells could be arranged to form a 13th in the series. Replacement letters could form MEMBER IN TOP JOB WILL SWAP.
All entries in the final grid are real words.
The Chambers 13th edition is the primary reference.

Across   1 Diminutive racer Hamilton’s made circuits of course in lead position (6)   6 Defeat for the bard when muse loses beginning of madrigal (7) 11 One who makes people late by turning to patter again and again? (8) 13 Potter finally cracks issue encountered reversing spell at school (8) 14 Scotsman for example collects 3 out of 4 possible points (6) 15 Fine the French after bust shattered (6) 16 Seizure of goods - after which American gang's busted (4) 18 Crier’s call filling shell of coconut shy in the extreme (6) 19 Furious about escapes from Syrian city cell (5) 21 Byzantine square bonces could have borne these? (7) 23 Laid around, turned over, right to left at first (6) 24 Mac's hay cart advanced round the bend leaving busy marketplace (6) 26 Boundless surge stops our opponents working miracles (7) 27 You might get this by ungathering one trimmed lasso (5) 29 Rook among group of birds missing last of pig swill (6) 33 Bowl over, bats over (4) 35 First couple of seamen smooth over bottom parts of ships (6) 37 Last one dropped dead, put in cooler (6) 39 Exceptionally large garment with openings to underplay my bony place (8) 40 Prior to November dreadful boat train's lower facilities made all who travelled late (8) 41 Ruffled nap ducks apparently developed for feathered part of skin (7) 42 Frequent flyer heads for Paris, lucky to be there in central location (6)

Down   2 Layabouts hide in lavatory with time wasted - that'll leave him upset? (6)   3 Happily complete circus comedian changing direction (5)   4 Historic city state briefly mentioned in article (4)   5 I let someone out—someone who's let out repeatedly? (8)   6 Onset of epilepsy treated with rest cure (5)   7 Poor Bambi’s missing one black foot (4)   8 Regular characters in in-depth, tense finale of Cagney & Lacey seldom heard (5)   9 Trains display time to go to Iowan city (5) 10 Opts for English desks once ballot-box goes missing (6) 11 Book for mass celebration - what nostalgic Birmingham expats might do?  (6) 12 Wrecks cap with soft lining (7) 17 Peg one bashes heavily (5) 18 Jumbles of calcium, potassium and einsteinium (5) 20 Minister mostly purged snobby chattering classes (7) 21 Unhitched from pillar, small vessel makes for small island (3) 22 Group run out of cryptic setters around the middle of thirteenth (8) 25 He flees, expressing hesitation about drunken duel (6) 26 Most gut rot is treated by pharmacist initially, it's psychologist's session that's designed to improve communication skills (6) 28 Organisation more sprightly with wings clipped? (6) 30 Leave rather small opening (5) 31 What's inside egg, gold bit having been tossed (5) 32 Part of arm protecting hand in a bust-up (5) 34 Bounder rolled up flush with success (5) 36 Poet’s greatly distressed having let letters go missing (4) 38 Maybe setter has upset stomach and temperature (4)

Credits Grid: John Nicholson and Andy Stewart Clues: Anax, Tim Anderson, Steve Bartlett, Rod Beards, Rod Bell, Shirley Curran, Brian Dungate, Peter Finan, Simon Griew, Derek Harrison, Margaret Irvine, James Leaver, Robert Lorimer, Kevin McDermid, Satyen Nabar, Nebuchadnezzar, Jack Nichols, Joe Nicholson, John Nicholson, John Nolan, Mark Oshin, Juliet Parkinson, Jeff Pearce, Rob Pinnock, Phylax, Ed Powles, Nic Pursey, Steve Randall, Rishikesh C G, Simon Shaw, Ian Simpson, Nick Smith, Peter Smith, William Snow, Sprout, Andy Stewart, James Taverner, Robert Teuton, Don Thompson, John Tozer, Vismut, David Ward, Luciano Ward, Nick Warne, Dave Williams and Keith Williams

Entries To enter this competition, send your entry as an image or in list format giving the final entries to ccpuzzles@talktalk.net before 8th May 2021. The first correct entry drawn from the hat will receive a book from the Chambers range, which has been donated by Chambers. Voting You may vote for your favourite clue with your entry. You can just nominate one clue, which will be awarded 3 points, or your top three which will be awarded 3, 2 and 1 points. The person whose clue accumulates the most points will receive a prize, which also has been donated by the Crossword Centre.