Voyage by eXternal

A significant number of clues contain a letter jumble, sometimes of two words, of items sharing a commonality, to be removed before solving. One aspect of these gives the origin of the voyagers, other aspects give one  name for the destination. The voyage is described by a message appearing in clue order from an extra letter in each of the remaining clues, to be removed before solving. Solvers must alter the final grid in line with the message.
    1    Homer's introduction to Iliad about slave island (7)
    6    Private secretary keeps faxes by one little box (5)
    10    Marine scientist's old boats can go to isle (12)
    11    Gopher statue eroded by river lay hollowed out horribly (6)
    13    Sent spokesman away from pilgrims' destination (3)
    14    Used choppers to seize border (3)
    15    After having cute son, usual to throw party for islanders (4)
    16    Remain wary, editor's outwitted (6)
    18    Powerful banker sold in the midst of retiring (5)
    21    Troop repeatedly use artillery to attack island race, English under sovereign's protection (6)
    23    Gathering dearth, alcoholic drink supplied to Fergus (4)
    24    Large planet is special celestial body (4)
    25    Struck with fear, MPs in Munich almost overwhelmed by donations (6)
    27    US grad astride seat on fire to review unit of brightness (5)
    28    Ran with religious man from range (6)
    32    Toff ultimately ignored bleak island (4)
    34    Repellent slob in street eating the Portuguese dung-beetle (3)
    35    Muslim ruler to somersault and flip (3)
    36    Sea bream and bass are to swim round Italy soon (6)
    37    Setter ensuring sonnies resolved inabilities to go further (12)
    38    Some larvae for a desert mosquito (5)
    39    Absolutely determined to write puzzle after latte (7)
    1    Cuckoo's chasing yours truly around British valley (5)
    2    One afternoon, note aquatic plant (5)
    3    Reasonable goals from three players outside area (4)
    4    Clove and lentil concoction, just one left (5)
    5    A cloud rising over earl's reefer (6)
    6    Gout to prick, leaving grand Indian city (7)
    7    Teen upset pious person with pig's heart in trough shaped like sword (7)
    8    Hebrideans topped Yemeni criminal coming round Loch Ness, northwards (7)
    9    Animal housed above Frenchman's compound (7)
    12    Scottish bird restricting aisle, to push forward (6)
    17    Poet's made darker as bishop blocked offer to bury dead (6)
    19    Ancient empire beheaded impertinent, openly weary revolutionary (7)
    20    A subtle medium for communicating speedily in hotel, perhaps (7)
    21    Ruin in islander's housing, mass of water completely filled (7)
    22    Small stag suffers flat cakes (7)
    26    Lace under control of farm especially celebrated (6)
    29    Party a Señora from the south backs (5)
    30    I must be in the clutches of drink, upset remark from partner (5)
    31    Made, possibly, to bear right and turn... (5)
    33    ...over a Scotsman's cargo flattened by wind and rain (4)
To enter this competition, send your entry as an image or in list format,  to before the 8th April 2015. The first correct entry drawn from the hat will receive a book from the Chambers range which has been donated by Chambers.