yep
ensure your bottle is totally empty, then undo the 2 grub screws in the side of the reg. Then slowly unscrew the top of the reg from the bottom, before the top comes off the reg turn it to the side so that the shims and spring pack dont fall out.
Once it is in 2 halfs, you should be able to remove the spring pack from the top half of the reg (make sure it stays in the same order), you should also have 1 or 2 silver washers, remove the silver washers and refit the spring pack, screw the reg back together and tighten up the side grub screws and refill the bottle.
the reg should now output at 450psi, to revert back to 850psi refit the silver washers.
HTH
bruce