bpy.ops.constraint.move_up(ctx, constraint="FOOBAR", owner='BONE') returns cancelled if the Pose Bone is not the active bone, despite all related context members are overriden:

ctx = bpy.context.copy()
ctx['constraint'] = con
ctx['active_bone'] = bone
ctx['active_pose_bone'] = pbone
ctx['selected_bones'] = [bone]
ctx['selected_pose_bones'] = [pbone]
ctx['selected_editable_bones'] = [pbone]

It only works if the corresponding bone is really made active using ob.data.bones.active

Sample setup: