Originally Posted by SalsaShark

So you are trying to put an adjustsble riser stem on a carbon steerer.
The problem you forsee is how to set the bearing preload on the headset unon installation. This is a valid concern. My guess is that this type of stem is designed for a fork with an aluminum steerer and internal starnut.
Without the internal starnut in the steerer tube, there will be nothing to pull the steerer up into the new riser stem and you will end up with a loose headset. There is almost certainly a bolt in the riser stem that is designed to thread into a starnut to accomplish the task of bearing adjustment of the headset.
Could you leave your current carbon expansion plug in place and modify it for use with the new stem? I see one potential option which requires the altering the top cap diameter of the expansion plug. For this to work, the top cap diameter would need to be reduced to match (or just a hair smaller) the outside diameter of the carbon steerer. This would allow the sleeve of the riser stem to slip over both the top cap and steerer as intended.
The question is whether or not the threading and pitch of the stem bolt designed to interface with the star not will also be able to replace the original bolt of the expander plug in the carbon steerer. This will have to be sorted before everything is put together, as the expansion plug will need to be assembled to this bolt in a relaxed position, and inserted into the steerer as the the riser stem is slipped over the outside of the steerer, all as one piece, making sure the expansion plug is pushed in flush with the top of the steerer tube. Once this is all put onto the steerer, you should be able to tighten the bolt, expanding the plug, pulling up the fork crown, compressing the headset bearings, and finally tightening the stem bolts.
Whether or not this is a good idea putting the extra leverage on a carbon steerer is debatable. You might be better served trying to find a traditional (non-adjustable) stem with as much rise as possible to avoid this mess of alterations to the system.