The more interesting question will involve some follow-on changes that I have in mind, like a .276 cal BAR. That'll be more involved, and fielded much much later.
This in particular I find interesting. The US went into the war relying on stocks of WW1 Surplus BARs. Production of new BARs didn't get off the ground until early 1944. If they want to maintain a unified caliber for rifle squads and have to adopt new-build weapons anyway, there might be an earlier competition for an infantry light machine gun to replace the BAR - OTL this didn't occur until 1939, and none of the entrants were completed in time to be of use, and were thus cancelled in favor of lightened M1919s. So in TTL with the .276 adopted in the early 1930s , a new LMG may be developed or licensed early enough for production to start before the war.