Is it possible to switch Reserve units/branches before attending BOLC?

Reserve transfers are pretty simple if there is another unit has a matching rank/branch slot.
Talk to the recruiter or retention NCO for options on reassignment and branch options. They can also verify any potential issues with your contract.

As a 2LT you have the opportunity to change but do it quickly or you will find orders for the re-aligned BOLC and a ticked off planning person in the Lieutenants in transition branch at Fort Knox.
You could also attempt to transfer to the National Guard in the state but that will need to be reviewed by the Army Reserve Regional Command prior to transfer and may be denied.
I switched branches and units in the Kentucky Guard, only to switch to Army Reserve later in my career. As CPT Garbarini says, find the retention NCO, they will have the power to login to the Retention Management System. You should be able to login to your Reserve account and review open slots. There is also the HRC https://selfservice.rcms.usar.army.mil/

I only have a minute to respond at the moment (so hopefully somebody else comes in with details), but just to ease your mind, yes. This isn't infrequent or unheard of, at least for Reserve Officers in Basic Branches. Until you graduate BOLC you are fairly fluid.

I can't speak to the State transfer portion though.

Did you ever find the answer to this? I am currently attempting to switch from QM to MP.

Have you looked at the Guard in your area? Not sure what branch you were “granted” with but the Guard may offer more options.

I don’t believe it’s a relatively tough process. Call the OSM for your state and see what is available. He could probably generate an LOA pretty quickly if there are open slots.

I have the same exact question as I near OCS completion slotted as a QM but I wanted to switch to MP before BOLC.

Where is your picture. stupid LT