Unfortunate for you because in this scenario you have to make a choice. Both exams are national level and there is no way there will be any change in schedule. Make your choice whether you want to be a civil servant and try prelims or you want to join law school and go for LSAT. LSAT entrance got rescheduled twice so there might be some possibility that it gets rescheduled again. Chances are not that much but still you need to decide and make your mind and put maximum efforts in preparation.