Where "High Gravity" begins is debatable, but for the most part, anything less than 1.080 to 1.090 can be re-pitched with no issues, either higher or lower. Much above that, what happens is the yeasts "mutate" that is they change the way they work. The changes allow the yeast to process the higher gravity/higher alcahol enviornment better without dying. Once the yeast mutate for the higher enviornment, they do not change back to "lower gravity processing mode" very easily.
Re-Pitch with no reservations!