Thanks to our modder, Futuretime23, who writes:

Download link is here, along with instructions.

Warning, the mesh swap isn’t free of bugs, and here’s a list of the currently documented issues:
1) Hair alpha transparencies don’t work, this is because I’m swapping default texture to get duke’s hair in and that doesn’t support alpha transparencies. A very ghettolike way of hacking duke’s hair, unfortunately necessary as otherwise no hair texture loads in for him.
2) His eyes and teeth have the hair texture in as they are not texture mapped by default – this is likely because 2009 duke, much like the 09 edf troopers drew from a pool of generic separate teeth and eye textures. This was likely changed for performance reasons if I had to guess.
3) His left leg bends a bit weirdly in certain animations, this is due to leftlegroll (a bone exclusive to 09 duke) weights not properly mapping to leftleg, so they had to be mapped to leftfoot to work.
4) Lefthandindex2 had to be mapped to lefthandindex3 to get it to work right, so you might notice the finger bending a bit different than what 2009 duke’s left index finger did.
5) No changes were done to multiplayer duke’s textures meaning his textures are currently a jumbled mess. To be fixed later.
6) Glove diff is an original design based off the 09 glove norm and spec – this will be replaced with an accurate recreation in the future.
7) Dismemberment and gibbing works fine, but the stuff that gets spawned is static meshes from retarget. There’s no static mesh equivalent for 2009 which means you get jumbled messes of gibs atm. To be fixed later in the future.

I haven’t done a full run of DNF’s campaign or DLC so I can’t comment if there’s any other issues.

Have fun guys!