Before I begin, you must know you have written a supreme piece of software!
Currently, I cannot see any way of editing the SIM Contact index number.
For example: the first entry can be dialed on the phone by entering 1#<call>; the 103rd entry by dialling 103#<call>.
Sony Ericsson saw fit to not include this capability in the phone, but I have seen this capability on other phones and phone management software before.
If you can implement this, I promise I will donate AU$25* and tell all my Sony Ericsson using friends to donate as well!
Thanks
* At current value of Australian Dollar... about €0.25 J/K