Relatively small repairs are generally not regulated, but many states have laws that require permits for installing gas appliances. In addition, some areas might require that work done with gas appliances and gas lines be done by professionals.
Gas lines present a risk of natural gas poisoning if leaks arise, and other appliances can cause gas in the air to ignite if it reaches a high enough concentration. In addition, gas appliances can produce carbon monoxide, a potentially deadly gas. For these reasons, many areas require training and certification for people who work with gas lines and appliances. However, small repairs to other parts of gas ovens are typically safe to perform without expertise.