Switching jobs in the Marine Corps?

I'm in the process of joining the Marines right now and I'm going active duty for at least my first 4 years and I'd like to go Infantry because I want the combat arms experience for a future job in the FBI. Now I also would like to be an Intelligence specialist in the Marines for the same field in the... show more I'm in the process of joining the Marines right now and I'm going active duty for at least my first 4 years and I'd like to go Infantry because I want the combat arms experience for a future job in the FBI. Now I also would like to be an Intelligence specialist in the Marines for the same field in the FBI plus the top secret clearance holds a lot of weight.

My question is can I go Active for 4 years as a rifleman then switch to reserve as an intelligence specialist or do you have to maintain the same MOS?

I'm going reserve for at least 4 years after my active duty time so I can be secure while I'm going to school and have a fall back if things don't work out.
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