This script will rename '(mirrored)' bones to their respective naming. Be sure to name one side of your unmirrored bones first with this naming convention bone_L_bonename or if you are working on the right side bone_R_bonename.
** Common workflow for making bones/mirroring
1) bone_L_arm is prenamed before mirroring via the bone tools.
2) the bone is mirrored with the bone tools.
3) the new mirrored bone name looks like this: bone_L_arm(mirrored)
** The script is used here:
4) run the rename mirrored bones script with those mirrored bones selected