Bones only update the rendered mesh, they do not affect the transform or collisions or other aspects of instances (aside from CFrame of descendant Bones). And Attachments cannot be parented to Bones, so you can’t put them in the Bone hierarchy.
However, Bones and Attachments are essentially interchangeable in-engine, so anything that can attach to an Attachment (or read/set a property on one) can do the same for a Bone.
So, if your Bone rig already has a Bone where you want the Attachment to be then you can just use that Bone. If the Bone is not in the rig then you can just add it. Or failing that, you can manually calculate the CFrame offset of your Attachment from a relevant Bone in the rig in its rest post, and then every frame at the appropriate time update the WorldCFrame of your Attachment to be Bone.TransformedWorldCFrame * AttachmentOffset.
(Also, I haven’t tried myself so take this idea with a grain of salt, but if you want to be able to move the Bone arbitrarily without affecting the rendered mesh you could in your 3D modelling application try setting the bone’s weight in the rig to 0.)