Despite being a decent update to the 2005 Cybertron/Galaxy Force Optimus Prime, there are a few things that the Siege figure just didn't do all that well or straight-up omitted. One was the shortness and proportions the figure that made him look too much like an awkward combination of G1/Cybertron Optimus with Energon Optimus' proportions. The DNA DK-13 upgrade kit helped out with that nicely enough. The other was that the Super Mode was the only way to display the GF/Cybertron Optimus form, even though it would have been pretty easy to make the backpack detachable while keeping the head plate and new chest piece connected to the robot mode. Then I wondered to myself what the best way would be to detach the backpack while keeping the mod reversible. I tried to remove the lengthy pin holding the head platform and backpack connect with a soldering iron, but it didn't work at all and I managed to burn a fingertip in the process. So I just started cutting a millimeter-thick section out of the grey part with a utility knife (which was surprisingly easy to cut though. IIRC it's that slippery and tough-to-paint POM plastic.) With this mod, the two grey sections holding the pin in place are now clips. Behold! Of course the mod still allows the two parts to be reconnected (albeit with a little bit of carefully-appled force.) I also took a hacksaw blade and a utility knife to the bottom of the track that OP's back kibble slides up and down on to make that piece of useless kibble removable, too. It comes off, tho it does get a little bit hung up at the end, but it's good enough for me.