@xris,
Cannibalism in species is normally relegated to the cannibalization of the very young, or the very old. I assume that if there is rampant (non-ceremonial) cannibalism there is an environmental reason for this.
The other problem I would have is that most cannibalism of the very young happens in species that have massive amounts of offspring in one clutch, which means that there is no rearing of said offspring.
So given the event that there is rampant cannibalism, and assuming that the same general biological parameters exist on the other planet as on earth. I would assume that the cannibalism is environmental and biological. Therefore it could not be changed. It would be like asking a snake to be a vegetarian. However if the cannibalism was purely ceremonial then, as a visitor you would likely not be subject to being eaten as long as you didn't pose a threat. Either way not posing a threat would be key because they would kill you anyway whether or not you were eaten.
So my approach would be to establish a non-threatening camp a considerable distance away from said civilization but not so far that they wouldn't find you. That way when they found you , if they didn't kill you, you would become a novelty. Build a rleationship of trust, either learn the language over a period of years or develope a trade pidgeon. Establish yourself as a valuable trade partner. Over the years start indoctrinating the younger generation inoccuously. Hopefully in a couple generations the non-cannibal pro-vegetable agenda will have spread.