Sharingan can copy techniques, such as seals and genjutsu. But things like Byakugan are pertaining to traits which are born into a user, these traits enable them to use their abilities of which are not able to be copied simply because the technique is something the specific user is born with (blood line), making it impossible to copy. This would also eliminate the ability to copy techniques used with traits such as Byakugan, because the Chakra highway will be different for each individual. So learning the Tenketsu attack against one specific person may be something a Sharingan user could possibly do, but it would only have application against that person hit with Neji's 64-hit Tenketsu attack, i.e. Neji/Naruto. That's purely speculation, though, and even then the ability to accurately disable Tenketsu would more than likely have to be done to the Sharingan user, since their more advanced techniques learned from using Sharingan come from seeing them used against the Sharingan user. At least, that's how I see it.