Is Shaving Brow Bone Possible?

You are correct. Most of the surgery on frontal bossing or prominence of the supra-orbital rim is based on FFS. However, these surgeons tend to be the most experienced. Concerns with entering the frontal sinus cavity make this a procedure that carries more risk than other common bone reduction surgeries. Fillers are an option for non-surgical temporary correction but the volume of filler required will make this somewhat costly to repeat on a regular basis.

Reduction of a prominent brow entails reducing the frontal bone overlying the frontal sinus.  Depending on the extent of bony prominence, which is a factor of sinus development and size, this may be performed by several approaches.  Mild-moderate bony prominence or bossing can be approached by burring or "sanding down" the bone.  However, severe bony prominence may require osteotomizing (cutting) the frontal bone and exposing the frontal sinus.  Depending on the anatomy of the frontal bone and sinus, it may be necessary to remove the mucosa or internal lining of the sinus to prevent subsequent infections with replacement of the removed bony segment and further contouring.  

This type of procedure should only be performed by a craniofacial surgeon, a plastic surgeon who has pursued fellowship training in craniofacial surgery and one who is properly trained to address the frontal sinus as well as the bones of the entire facial skeleton.

There is no place in this type of pursuit for the use of fillers. A filler would only serve to transiently camoflage the prominent brow by increasing the prominence of the bone on either side of it or above it.  This is not a solution but a poor illusion that will only result in the patient now concerned that an even greater segment of their brow/forehead is too prominent.