I wouldn't have expected this to work on Linux/Unix, so was surprised when it sounded like it might on XOS. In linux, as soon as a command is run that would disconnect your current ssh/telnet session, the batch file exits.
Can you create another vlan with it's own IP temporarily for the purpose of changing the default vlan's IP? create the vlan on the target switch and the switch it connects to, ssh give them both IPs in the temporary vlan, ssh to the target's temp IP from the other switch, change default vlan's ip, destroy temporary stuff.