How likely would an active duty Air Force 2nd Lt. be able to inter-service transfer to the Marine Corps Reserves as a pilot?

It’s fairly common to transfer between services. Especially on the Reserve/Guard side. I know many folks who transferred from the Marines to the Air Force and Army, but I know of no one who went from another branch into the Marines. Transferring to the Marines from another branch is uncommon. Mostly because the Marines don’t issue waivers for training. In other words, if someone went from the Army to the Air Force, the Air Force would not require them to attend USAF basic training. They would accept the Army training. However, it’s my understanding that the Marines require everyone to attend USMC training regardless of their previous experience. At least that the way it used to be.

A Marine officer recruiter could probably answer the question better though.

You would need to go to OCS and TBS. Depending on the airframe I believe you’d need to re-train to earn Naval Aviator wings.

The required lobotomy usually makes those interested do an about face, so no one knows for sure, lol! JK, good luck.