Compound radius necks are made on a machine. Typically the machine is a swinging arm with pivots at 16″ on one end and 10″ on the other. We have a machine like that here. It is for all practical reasons impossible to put a linear compound radius on a neck, sanding and shaping it by hand. The expense of doing that would be astronomical and pointless.
When refretting a compound radius it is like refretting any other neck, with the caveat that one must have the experience to level a compound neck properly by hand. It is done with a leveling bar and an accurate eye for detail. On extremely worn necks it may not be possible to level it and it may call for being radiused to a 12, 14, or 16 inch radius. Those are the rare exceptions but you should be aware of it.
Why not put the neck on the machine and re-radius it there? Because the machine is aggressive and has a large potential to ruin the neck, and there is no turning back to undo it. Next, the setup time to go from different compound radiuses is prohibitive in terms of cost of labor. You could easily purchase a new neck for the time involved in doing that.
We have refretted many compound radius necks with stainless steel frets and have very happy customers. We have the knowledge and skill to do it properly it is not something new to us.