In my experience climbing in the Ecuadorian Andes, it was better to stay mostly primal, only slightly increasing my carbs (as I might before any extreme endurance activity anyway). I think it is more important to fuel your body with what it's used to being fueled with, because if you've been primal/low-carb for a while and all of a sudden ramp up the carbs, your body is going to be like "wtf man?" Drinking lots of extra water is essential and very helpful with acclimatization, but extreme diet changes are unnecessary, in my opinion. Take it easy the first few days until your body adjusts, and depending on your travel itinerary, try not to make extreme elevation changes (beyond the initial change of just going there) too quickly.
Also, unless you're going to be at really high altitudes (16,000 ft or higher), I wouldn't worry too much about having serious altitude sickness problems.
Try cuy if you get the chance