Interesting musings NOMISYRRUC, now as to the other side of the coin, how do the japanese react to Constellation &co plus the aviation increase? Can they push earlier some of the shadow conversions, order more planes like B5N2 (which was historically produced only up to August 1941 at Nakajima, the production stop being cause of sever OTL kanko shortages in 1942; production only restarted in spring 1942 at Aichi and then Hiro)? Or maybe they cancel one of the Yamatos of Maru 4 keikaku and build a proper carrier instead?! (or so i wish)
Btw, regarding the premise of CV-9 Constellation, the stronger reaction to Panay incident does it include an oil embargo?
To answer your questions in reverse order.
No it doesn't include an oil embargo. If it did the Japanese would have to back down or start the Pacific War 3-4 years earlier and I don't want that to happen because it would void the thread.
Having said that I read in one book about World War II that the oil embargo was included in the 1941 sanctions package by mistake! Is that true?
To answer the first part of the question I don't know. I interpreted the question as the Americans have one extra aircraft carrier in 1941, but the Japanese have the same number of ships. I think the Japanese should have done some of the things you suggested regardless of what the Americans did, plus some things that you haven't suggested. One of which is that Hiyo and Junyo should have been built as Shokaku class carriers. If the contracts are taken over in 1938 instead of 1940 as in OTL that might be possible.
However, Congress increased the aircraft carrier force from 135,000 tons to 175,000 tons in 1938 as a reaction to Japan ordering Zuikaku and Shokaku in 1937. If the Japanese had built 4 aircraft carriers in 1937 instead of 2 aircraft carriers and 2 battleships the Americans would have replied by increasing the aircraft carrier tonnage by 80,000 tons in 1938 and ordering 4 Yorktowns instead of one in the real world and two ITTL. In 1938 the USA probably had the resources to complete 4 Yorktowns by the end of 1941 without building fewer battleships and cruisers.
Furthermore if the Americans find out that the two large liners being built for the Japanese are actually fleet carriers they might respond by starting to build the Two Ocean Navy one or even two years earlier.
The other things I would have done to make Japan better prepared include having the IJN expand is aircrew training programme, build more merchant ships before 1941 and reorganise the shipbuilding industry for the mass production of merchant ships and convoy escorts after war breaks out. However, these preparations enable Japan to fight a long war more effectively. This is not so that they can win a long war, they can't. However, it might create a stalemate that lasts long enough for the American public to tire of the war and force the US Government to make a negotiated compromise peace.