I don't know what country you're talking about, but here in the USA, there is no requirement that a person even has to obtain a license or certificate of competency to become a farrier, never mind any "code of conduct." The American Farrier's Association has a certification program, but it's entirely voluntary and it only relates to competency in different aspects of shoeing horses. This is information about the certification program: http://americanfarriers.org/certification/
(FWIW, the absence of any licensing or certification requirement for farriers has been an ongoing headache for the horse industry. Any fool who can buy the tools can advertise himself/herself as a farrier, and believe me, there are some real butchers out there. They don't usually last long but can do serious damage to the unwary.)
The only licensing requirement I know about for farriers is for farriers who want to work at the racetrack. Those farriers have to undergo licensing, and as with all people who work on the backstretch of racetracks, have to undergo a background check for felony convictions and criminal issues.
With regards to a code of conduct governing personal behavior, maybe it's different in other parts of the country, but here in Southern California where I live, most of the horse owners I know of want someone who will do a good job shoeing their horses and really don't care about their shoers private lives. They want a shoer who will show up when he/she says he will come out, who does not handle horses roughly, who does a good job trimming and shoeing and whose charges are reasonable.