It depends on how much higher, how long before you drop it, how much you drop it, and how quickly you drop it. If it is too high for too long, you can get some sharp alcohol, solvent-like, or fruity flavors. How long is too long? Hard to say, but remember that once vigorous fermentation begins, most of it is done in the first 48 hours after that. Also remember that a byproduct of fermentation is heat, so if you have a wort that is too warm already, it will ferment fast and produce even more heat, compounding the problem of getting it down into the range you want. If that happens, you want to cool it fast. Problem is if you cool it too fast and too far, your yeast can shut down.
Best bet is to start your yeast in your wort near the middle to top of the listed range of the yeast (usually about 70F). If unmonitored, the heat produced by fermentation will easily heat the wort to 73F or 74F (possibly higher), so at the first signs of fermentation, start cooling the wort to the lower to middle part of the yeast's optimal temperature range (usually around 65F to 68F, but it varies). Note that to get it to 65F, your fermenter's external temperature needs to be cooler than that because of the counteracting heat produced by fermentation. A good way to do that is to put the carboy in a small water bath with a towel draped around it that is wicking water up from the water bath.