Change Informix Serial Number??

Hello, We have a couple of valid Informix instances that are also covered by support contracts. But now, we are removing one of the supported instances from operation and would like to transfer the serial number of that instance to one of our unsupported (but licensed) instances. Apparently it is a hassel to have Informix change a serial number listed on the support contract so this might be an easier way arrange support for the unsupported instance with the supported instance being taken offline. Is there an easy way to change the serial number returned by onstat? I've already looked in the onconfig file and it isn't listed there, but perhaps there is another simple place to make the change? Is it contained in the sysmaster DB? If anyone can recommend an easy way to change the serial number, I would really appreciate it. Thanks! Brian