Today’s update to RuneScape makes it possible for players to reset select combat skills, only once, by talking to Nastroth in Lumbridge. Choosing either option will result in associated skills being reset to level 1, and all associated rewards and quests that required said skill being revoked. Jagex has cautioned that skill resets cannot, and will not, ever be reversed under any circumstance.
As a security precaution, players who have no intention of ever using this feature, but are afraid of the potential for malicious use, can talk to Nastroth in Lumbridge and disable the feature on their account permanently. This option, similarly, cannot be undone.