Me too, which is why I haven't done it yet. That said, I find myself wondering if the caution is overblown, despite the warning to disable the tilt function on the third-party sellers product pages typically being in red and all caps, since Herman Miller itself appears to offer 'standard tilt' as an option when you buy the thing in its drafting stool version to begin with. (Herman Miller's site doesn't really seem intended for individual consumer self-service, though -- it'd probably be best to ask a salesperson or something.)

Edit: I called Herman Miller customer service and the rep confirmed that Aeron drafting stools don't have any restrictions on reclining. She couldn't speak to the use of third-party kits, of course, but it really seems like that warning is more of a CYA thing than a real danger.