What warning difference? It's hard to find any definitive answers, but the case happened in 1992. Based upon my own recollections, this was the time where every fast-food chain started putting warnings on everything. McDonald's even added warnings to their hot apple pies and other "served hot" foods.
Would Liebeck have acted differently? That's not the objective of the jury in this case, especially considering that McDonald's conceded that their warnings were likely inadequate. To the extent that it is relevant, the jury did find Stella Liebeck 20% at fault for the accident and so the damage award was adjusted accordingly.