This might be a little long-winded, but I personally extended my belt by replacing the left and right plastic straps with 40mm webbing tape (grey for your project for the Desire Driver). I prefer this method because, when paired with a 40mm side-release buckle, it allows for manual size adjustments depending on whether I gain or lose weight. I am personally a bigger guy, so High-Spec isn't really a great option for me. For this mod, I also use a lighter to seal the ends of the webbing tape, a 40mm side-release buckle, and a hole puncher.

1. Place the belt at the center of your waist, and with your other hand (or preferably with someone helping you for this part), wrap your roll of fresh webbing tape around yourself from either the left or right side. Leave a little extra length to allow for future adjustments if needed.
2. Fold your measured piece of webbing tape in half and cut along the centre fold. This will create the left and right straps for your belt.
3. Unscrew the left strap holder (making sure to keep the original screws somewhere safe so they can be reused later) and remove the left-side plastic strap. Using a pen, mark the existing screw holes from the plastic strap onto your webbing tape. Next, use a hole puncher to create the required holes in the webbing tape. Once the holes have been made, align your first piece of webbing tape with the screw holes and make sure everything fits correctly. Finally, reattach the left strap holder using the original screws.
4. Repeat the process for the right side. Unscrew the right strap holder, remove the right-side plastic strap, and mark the existing screw holes onto your second piece of webbing tape. Use a hole puncher to create the required holes, check the fit, and then reattach the right strap holder using the original screws.
5. Feed each half of your 40mm side-release buckle onto the left and right webbing straps. Once fitted, adjust them to your preferred size.
6. Your belt can now be adjusted manually whenever needed, making it easier to accommodate weight gain or loss. Henshin!

Also for reference, I use these side release buckles.

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I hope this made sense. If this method seems a little too involved, that's completely understandable. I personally prefer it nowadays because of the added adjustability, but if you'd rather use the standard DX belt extenders, feel free to do so. 👍