The word "up-setters" can be replaced with a number of different synonyms, each with their own nuances of meaning. Some alternatives include "troublemakers," "agitators," "disrupters," "rebels," "instigators," "provocateurs," and "mischief-makers." Depending on the context, one synonym may be more appropriate than another. For example, "rebels" may suggest a more intentional and organized resistance, while "mischief-makers" may connote a more playful or less harmful disruption. Ultimately, the choice of synonym will depend on the tone and intention of the writing, as well as the specific situation being described.