OK, I know that you enlist into a particular slot in a particular unit when you join the Guard. But what happens when you want to change MOS?

I understand that if you want to change units, it's up to your current command to allow you to leave - but what if the you want to change MOS within your current unit (assuming an opening exists within the unit for the MOS you want)?

Is it still up to your command to decide whether or not to 'release' you from your current slot?

And who makes the call - what if I want to change companies within a battalion to get the job? Is it a battalion or company decision?

Are active army In/Out calls at all relevant?

Thanks for any info.