Looking at the code on line 246
SOAPEnvelope.payload += "<updates><Batch OnError='Continue'><Method ID='1' Cmd='Update'>";
I made a quick change on my local copy to read,
SOAPEnvelope.payload += "<updates><Batch OnError='Continue'><Method ID='1' Cmd='"+ opt.mode +"'>";
Then added a mode: "Update" or "New" to the function call, which worked nicely.