Is it possible to reclassify into an MOS and become qualified without attending AIT?

Last I checked, there was a way to reclass if you have worked in the MTOE position performing the duties of that position for a certain amount of time. I don't know if that is still a thing though.

I do not know if this still holds true, you would need to check with your S1 Personnel Section to confirm and begin the process. Depending upon the MOS you were to reclassify into You could complete the required Army Correspondence Course, upon success full completion the S1 and Unit Commander could submit the forms for reclassification and the new MOS awarded based upon that. That process as mentioned earlier could also be part of a 2 Step process where you would need to attend a Phase II school provided by a Reserve Training Site.

Another option had been to hold Specific and Certified Civilian Skill Sets that are also employed by the Army. Civilian or DoD Firefighters in GS0081 positions with full certifications at or above the vacant pay grade could be awarded the MOS of Firefighter. Similar held True for Heavy Vehicle Operators, tractor trailer drivers. I had been a DoD Civilian Firefighter/EMT and concurrently held a Class A CDL license with endorsements for Doubles, Triples, Tank Vehicles, and Hazardous Materials.

If you are Active Duty, consider options open through the Education Center on you base as well. Your S1 again should be able to assist you if the Ed Center offer courses that are applicable to the MOS you're looking to transfer or cross level into.

Much has changed since I retired from the Reserves in 2001, and a DoD position in 2007. And ask your Platoon Sergeant as well she or he should be able to give guidance.

I don't see it happening- I mean the whole point of AIT is to train you in your MOS to the standards of today- I could see if it was a prior MOS you had held- Have you asked to see if this MOS has an on-line component or is offered as a correspondence course? I took my secondary MOs that way 100 years ago.