yes it can be done but I would think about just getting a complete upper and being able to shoot both easily

Yes sir, it's not terribly difficult if one has a torque wrench and barrel nut wrench. The bolt carrier group and magazines that came with the gun will work just fine with 300 BO.

Chris, yes, You can convert any standard 5.56 AR-15 to .300 AAC Blackout by merely changing only the barrel. I would use these for feeding reliability as well : budsgunshop.com/catalog/product_info.php/products_id/714017896/magpul+pmag+m3+300blk+30rd+blk

Yes, but you may have to get 330 Blackout magazines (Magpul) and change the spring and buffer.