Alright assuming that it is possible, when does it happen? I would put a likely date as around 1500BC or so, because I think that some kind of Mississippian civilization would domesticate them first, and thats about 500 years before the Adena Culture and 1000 years before Hopewell culture of OTL. This would give them time to have the *Buffalo become part of there basic agricultural package. Any one else have a different opinion?
If so then this has several benefits for the Mississippian cultures of OTL. In OTL there only domesticated animals were the turkey and the dog, and they didn't make a Food dog like the Aztecs severely limiting their protein intake. This *Buffalo would be useful not only for plowing fields, but as a major source of protein for the Mississippian cultures, meaning that they will not (as in OTL) venture out for miles to find animals for hunting. The *buffalo will then become a definite major part of their life. Will there milk be suitable for human consumption?
It will also spread to the Great Plains very quickly (by 800 BC minimum), which will lead to a more densely populated Great Plains. There they will overtake dogs (I imagine) as the main element of plains life, not only being a source of transportation (travois pulling, and perhaps a bit of riding for the smaller peoples, I don't think they'll have wagons, yet) but also of milk and meat which they generate by eating grass which is all around them. They'll easily become the most important possession of any family. The closest analogue I can think of are the eastern African cow herding peoples, with their lack of horses (I think. I'm no expert on this), but these people will have far larger grounds to pasture there animals.
It will be more difficult to get them to Mesoamerica, but it is not an insurmountable challenge. I think the most likely way will be south along the Gulf Coastline, as I don't see much travel over water. It will take some time, but I think a conservative estimate would be around 1 AD or so. Just in time for Teotihuacan and Monte Alban. Teotihuacan in OTL was the massive precursor to the Toltecs and Aztecs that ruled much of highland Mexico from their base in the Valley of Mexico. They collapsed around 600 AD in OTL. In ATL they are likely to become more centralized with the creation of roads for *buffalo pulled carts, plus the addition of a valuable source of meat and milk, allowing more marginal areas to be cultivated. Perhaps they'll last longer?
Done thinking now, maybe if anyone else interested I might continue this.