If I am in the army reserves and join ROTC in my college, will I have to change my MOS ? Or will I have a option to change my MOS?

Once you contract into ROTC you must join the SMP (simultaneous membership program) to continue with your unit. This is be ause you will now belong to your ROTC unit, not your reserves unit, and several legal things in your status change. You can continue in ROTC for a while without having to contract, speak to your cadre about what options are best for you.

Once in the SMP your MOS changes because your contract with the army has changed, you are no longer enlisted. Your MOS becomes 09R, which has little to no meaning. It seems to serve as a place holder just so CMDR'S can shuffle you around given their needs and slots available. It's a fantastic option and I can almost guarantee you that you will make more money once you join SMP.

First thing, having went to IET and having an MOS will exempt you from the first two years of ROTC. I can see no advantage for prior or reserve service members to attend the first two years. Then joint as an SMP Cadet in your junior year. Complete the last two years and compete with the rest of your class
for the available slots in the branch's that you are interested. When you go to SMP Cadet, you will get paid at E-5 for your drill time, you will have more experience than your peers, and on the completely mercenary point view, you don't lose any time in service and will be paid at O-1 with however many years of service. If you aren't looking for Reserve duty, don't sign up for a Guaranteed Reserve Force Duty scholarship.

Remember also when you join ROTC your duties and responsibilities will change. As a Soldier you are responsible for getting your job done, but as an Officer your job is your Soldiers and the mission. Once you Commission then you will be Branched (Officer version of MOS) as an Officer.

If you are in the reserves and do ROTC and commission in the Reserves you can basically get whatever branch you want as long as you qualify and have a unit that accepts you.

Alot of good pieces of advice to your question on here PVT Ngo. I take it your probably using your GI Bill to pay for college as is. But you did not say what year you are in college, so you got answers that covered the whole gauntlet for you - and that is really good. If your a sophomore - you may want to look at doing the 200 series level of ROTC - while staying with your unit until your Junior year. COL Thompson makes some good points of the advantages of that in the knowing the other cadets and the staff. When it comes time to be an SMP - I had dozens through the years - and their MOS really was no longer their real task (minus the intel folks - who often stuck in the S-2 shops) as much as the task is so many aspects of leadership. If your PSYOP or CA - same thing - likely working with CO or BN HQ staff. When time comes for commissioning - you put your picks in ranked order - and someone determines which branch you start out with. If you stay in the USAR - you do have a lot more wight in your choice.. but needs of the Army always are there.

The reserves will treat you like the regular Army. When I became a SMP cadet (contracted) I kept my old MOS but when it came time to commission you will fill put your wishlist and will go needs of the Army. If you want to guarantee a special branch you can go National Guard which allows you to guarantee a branch but there are plenty of drawbacks with the NG.

Most of my peers that were in ROTC and NG/Reserves continued their duties and responsibilities in whatever their MOS. Their commander did disciple them a little more to prepare them to commission. The only way your MOS would change is if you became an SMP cadet, a 09R.

If you are planning on remaining in the USAR and contract as a cadet, your MOS will change to 09R (Cadet/Officer Candidate). Participating in both the USAR/ARNG and in ROTC is called the Simultaneous Membership Program (SMP) and you will likely no longer be performing your previous duties and instead be assigned an officer to shadow.

To answer your question of if you will have the option to reclass, unfortunately no. All contracted cadets have the 09R MOS as a placeholder until they are branched between their junior and senior years.