I found a link from 2 years ago
1) NEVER cut the mains and leave the crosses on 'cause it can easily break the racquet head
2) You can try putting the racquet on the stringing machine BEFORE the croses break, then cut the crosses and replace them. But it's risky.
3) If you break crosses/mains you must immediately cut all the strings so that you not put your racquet to uneven stres