The administration of Gov. Dannel P. Malloy, which is under a court order to desegregate Hartford schools, is attempting to redefine a segregated school – from one that is more than 75 percent minority to one that is more than 80 percent minority. The change would raise the threshold at which the state is responsible for stepping in to desegregate a school. It might also, however, allow about 300 more Hartford minorities to leave low-performing city schools and enroll in some of the region’s themed magnet schools. Or, some of these 300 students might stay in their existing school, which would be considered integrated under the new standard.