If HA paste is placed on the cheekbones, can this be shaved off a year down the road?

Cheek Augmentation is usually performed using implants. However, some surgeons use HA to augment the cheekbone. Yes, the hydroxyapatite can be removed. An incision inside of the mouth is used. In person consult will be needed to determine the feasibility.

While HA cement never truly becomes bone, it does get integrated with bone around it particularly if applied as granules. Its secondary removal can be done, as you have suggested by a shaving or bone burring technique....provided that it had to been placed too far posteriorly on the cheekbone.