Once the main fermentation is complete, you shouldn't have to worry too much about a rise in temperature. A cooldown could be a problem by potentially causing the yeast to flocculate before fully cleaning up after itself, but warming at this stage shouldn't create undesirable flavors and may actually give the yeast a kick in the pants to speed up the cleaning (though I haven't heard this sort of thing recommended except in lagers - known as a "D rest").