Evergreen by Flowerman

In sixteen across clues, a letter needs to be removed before solving, always leaving real words. In clue order these spell out advice to help the solver locate and highlight two thematic items (11 cells - 2 words separated, and 5 cells).
In six down clues, a letter in the wordplay must be removed before solving and inserted in the wordplay of the next affected clue or, in the case of the final clue of the series, inserted in the first affected clue. Letters leave and enter different words, and real words result from the changes. The removed letters in order spell out a word which, together with a word in the grid, form a product of the theme. The word in the grid can be found using the advice above and must be highlighted.
One entry, which can also be found using the advice, represents one word of an additional two-word thematic item. As well as highlighting this word, solvers must show that they know what the other word is by highlighting two examples of it (both 4 cells). One is an entry and the other is a partial entry.
Finally, solvers must highlight the theme (13 cells).

Across
    1    Bard ropes in a servant finally to deliver son’s medication (8)
    6    Permanent prize backed by karate academy (5)
    9    Unit deserted after drummer went on and on (6)
    10    A fitter upset with old associate forgetting about vessels (6)
    13    Estimation of supplies detailed on time (6)
    14    Tenor out of pocket? It's astonishing (6)
    15    Dental duo dealt with swellings (9)
    16    Fish in one’s crate primarily caught off Dover (5)
    18    Sound tense entertaining international artist (6)
    19    Is Norma accepting chancellor’s rock? (7, 2 words)
    21    Information sent back about universal joints (5)
    23    Primate regularly marking canons (4)
    25    Reportedly Jock’s packing is orange (5)
    26    An amount of moonshine left (4)
    27    Tabu ignored by adaptable old magistrate (5)
    28    Girl extremely taken with positive boss (7)
    31    Yuppies not content to get into queue for amino acid (6)
    33    Eccentric rated after having succeeded in disabling weapon (5)   
    35    City with 42 title thanks actress (9, 2 words)
    37    Wild sheep on moor turned tail after Troy fired (6)
    38    Are sailor’s nets for Will’s attacks? (6)
    39    Communist member finally tore up card (6)
    40    Grump perhaps acting appallingly in the middle of an opening (6)
    41    Grasp and tie silk cloth (5)
    42    Ann cracking jokes at start of egg-and-spoon race (8)
 Down
    1    Lord! Dutch women wanting me to feed a bull (6)
    2    Gunners crossing over pass to provide help for a group (6)
    3    Bad for an Australian ring to shun canine breed (5)
    4    Officer putting down a proposal (4)
    5    In eastern Iran it is ultimately not prudent to gossip (6)
    6    Yogi prayed to be reincarnated? Not ever, according to some genius (7)
    7    Game over, Toni’s sacking nurses (7)
    8    Mostly store mother’s minced beef (5)
    11    Hounds and gun dogs passing badger’s burrow? Hard to say in advance (7)
    12    Gents in favour in Albany (6)
    13    Conservative Catholics closing in on identity for insect (6)
    14    Retire to an ancient English property beside river (7)
    17    Gran taking out special teat perhaps to supply foodstuff (7)
    20    Authorised to underpin very good petition (7)
    22    Sponsor endlessly turning up to support university organ (6)
    23    Blake repeatedly breaking into sound of om relaxed (6)
    24    Curie determined to zap the terminal section of a chromosome (7)
    25    Strangeness in governing body detected by faculties (7)
    28    Ray pinching queen’s sacred text (6)
    29    Smooth and cylindrical core discarded by the network (6)
    30    Cinephile’s focus is on train leaving Norway in mystery (6)
    32    Once driven to turn off at end of highway (5)
    34    Food ends up on Tony’s foot (5)
    36    Except for The Sun, mark press down (4)

To enter this competition, send your entry as an image or in list format giving the highlighted entries and the theme to ccpuzzles@talktalk.net before 8th July 2019. The first correct entry drawn from the hat will receive a book from the Chambers range, which has been donated by Chambers.