Getting a player from Blue Lock to play with Sae would definitely prevent the U-20 from getting Rofl-stomped so easily.
I mean obviously they're still gonna get stomped since only Sae and the Blue Lock pick would know what's up, the coach is a shit bird on the same wave length as the association and the boss, and if I had to bet, I'd bet that blondie that got eliminated with a face shot at the beginning would be on the team to make it more interesting.
But even if now, the U-20 team will be made of people like that blondie that plays shitty football. The big question will be if Japan's traditional strength in the mid and back field will be enough to repel a team of aggressive forwards.
All things considered, doubtful, but still.