We have had lots of occasion to use Stockholm tar, it is great for helping to heal a wounded chook, although it seems to slide off bigger gashes

. It certainly wont stop the pecking by any means though.
We are down to just two chickens now, neither of whom lay, one is permanently bald and we tried everything including bumper bits, having the vet clip beaks, sprays, lotions and potions but in the end we gave up. We are just biding our time now until we can get some bantams, I know it sound horrid but they are just taking up space we do not have and are non productive. and have been for over a year
One other thing is make sure you wear disposable gloves as it's an absolute pain to wash off anything.