There are two section for restoring device-specific IMEI number on UIQ2.x devices. One of them is a plain text file which is named "plpvar.ini" and located under "c:/system/" folder.
As I said, it is a plain text file so you can easily modify it. But after every reboot, it restores default from modem section.
Also this modification doesnt affect modem's IMEI. So if you want to check modifiton from dialler (using *#06#), you cant. It is only useful for applications.