Generally speaking, Tocharian was not quite a game changer.
Tocharian languages are the most-eastern IE languages; and yet they belong to the centum group, although they share with the satǝm group at least one phonetic feature – the unrounded velars where the western group has labio-velars. Tocharian shows us clearly, that the reconstruction of PIE is still incomplete.
Some word forms confirm old PIE etymologies, and, at the same time, they raise new questions. Ex. g., the ‘earth’-words: To. A tkaṃ, tkanis with an initial dental stop like Hitt. tegan. Does it prove that Greek χθών had undergone a metathesis? If yes, why did this metathesis not occur in To. tkaṃ, keeping in mind the To. ‘tongue’-words A käntu, käntwis, B käntwo, käntwa, which look like they had been transformed by an old metathesis of the stops – cf., ex. g., Go. tuggo?