Put the rear half of the bolt in a vise, between two soft whatevers, then using the bolt handle, simply unscrew it. As you're unscrewing it you'll need to apply a little pressure as if you're trying to push the halves together. There's a spring trying to push the halves apart. When you get to the end of the threads you need to make sure the two halves don't get pushed apart before it's unscrewed, and thusly eliminate any chance of doing damage to the threads.
Then when you re-assemble it you simply push the two halves together as you screw them together. Easy as 1-2-3.
Then when you re-assemble it you simply push the two halves together as you screw them together. Easy as 1-2-3.