Well, the Brits did fix the Corsair to suit their requirements. Clipped wings, raised tail wheel, centre-section drop tank, etc.
Vought lengthened the tailwheel strut when they made some changes to the F4U-1. Other changes were raising the seat seven inches and replacing the birdcage canopy with an improved version - this became the F4U-1A.
The FAA received their F4U-1As from Vought with clipped wings (eight inches removed), so they'd fit on RN carriers.
So, Vought in fact fixed for Corsair to meet FAA needs. That makes more sense than chaps with hacksaws at RNAS Yeovilton.
Let's just look at that in a bit more detail. Extracted from Dana Bell's books on the Corsair and others.
The first Corsairs to go to the FAA were 95 "Birdcage" F4U-1 Corsair I, that were delivered from May to Sept 1943. The vast majority of these were delivered to training units and then new squadrons forming in the USA. Only a handful were immediately sent to Britain, although some more followed later.
The first 230 Vought built F4U-1A Corsair II (delivered Aug - Sept 1943) and the first 74 Brewster built F3A-1 (delivered Jan-Feb 1944) also received the original wing. The Mk.II began to arrive to replace Mk.I on 2 of the first 3 squadrons to form in the USA in Aug 1943.
It was quickly noticed that folded, these would be too tall for the hangar decks of the 3 Illustrious class carriers they were intended to operate from. So
Brewster (as a special project, not Vought) devised a short plywood wingtip and a method for for cutting the original wingtip off the wing (as originally designed the Corsair outer wing panel from wing fold to tip was constructed as a single piece. That changed later). Hence the story about needing to take a hacksaw to the wingtip to make the modification. Andover Kent Aviation then designed a fibreglass replacement for the plywood one. It began to retrofit these to FAA Corsairs from Aug 1943 in the USA. That shortened the wing to just inside the outermost rib.
Dana wrote:-
"All British Corsairs that hadn't already been destroyed or shipped overseas would eventually be refitted with the shortened tips."
Production Corsair II & III built after that and all FG-1A/D Corsair IV built by Goodyear (deliveries from July 1944) were given a shortened wing tip on the production line. But that was a tip that was even shorter than the Brewster / Andover Kent Aviation design.
Between 6 & 17 October 1943 the first 3 Corsair squadrons to form 1830, 1831 & 1833 (only 1831 retained Corsair I at that point) and a batch of replacement aircraft were loaded on the escort carriers Slinger & Trumpeter at Norfolk, Virginia. They were disembarked at Belfast on 1 Nov. 1831 was disbanded on 12 Dec 1943 with its personnel being used to enlarge the other two squadrons. 1830 & 1833 first went aboard Illustrious in Dec 1943 for deck landing training. The next 3 squadrons received Mk.II in Oct-Nov 1943 with 2 leaving for Britain in mid-Dec (the third disbanded in the USA to create a another Corsair training unit).
So there was plenty of time for the clipped wing tip to be retrofitted to early FAA Corsairs before they left the USA for Britain. Now whether British maintenance personnel helped out the Andover Kent boys with the modification we will probably never know. Certainly by the time the first went aboard Illustrious they had the clipped wing tips.
Work on the the centreline fuel tank was begun by Vought in Dec 1942 and by mid-1943 Brewster was involved in a bomb rack conversion as a special project. Vought produced 86 conversion kits for the earliest Corsair Mk.II to come off their production line (Aug-Sept 1943 production). It is possible that these kits were fitted by British personnel. This became a production line mod around this time.
The more I think about this myth, the more I get the feeling that many of the mods developed by Vought took time to filter their way through to the FAA and were then being retrofitted to aircraft by FAA personnel at Royal Navy Repair Yards or even on the carriers themselves as they became available. Norman Hanson in his wartime memoir, records how at one point in April 1944, the squadron flew their Corsairs from Ceylon to southern India to pick up a batch of replacements (he says to pick up a later Mark, but Illustrious' squadrons didn't get the later Marks).