Can it not be achieved by fitting Dog Bones ? I say this as my brief ownership with a X-ADV 750 had dog bones fitted to lower the bike.
If so I am sure there are a few engineers out there who could machine you up one or a pair ?
The 400 has a lever system and the steel part (Dog Bone) between the shock and the frame can be made shorter or longer a little. On the Eco-Exo Forum Roger B used a 2008 AN400 and found the shock mount would not raise the back of the trike and it would bottom out on big bumps. So he had a machine shop make one about 1 inch longer. It was a PITA to install but it gave him the extra 1/2 inch raise so not to bottom out.It could ......
However, the "dogbones" (links) are not individual items, but a fabricated assembly (Item 12 below). Could be cut and shut with side plates welded onto the existing links?
Extreme care would be required to maintain alignment of the mounting holes.
The result would mean less clearance between the rear wheel and the trunk base. Not much there as standard, on full bump, so.....
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I think the result, if it did improve OP's comfort, will detract from the scoot's handling.