Posting this from Xda Developers.
The fastest easiest way to debrand your X10 to Nordic firmware fo rthe Eclair update due out today.

Quote:
1. Root your X10i/a (See other posts)
2. Download Root Explorer.apk (market)
3. Open Root Explorer and navigate to /SYSTEM
4. Push on white button in the right top corner of Root Explorer (This wil change R/O in R/W).
5. Long Press on the file Default.prop and choose "Open in Text Editor"
6. Change in the folowing lines the XXXX-XXXX (scroll for firm codes):

ro.semc.version.cust=XXXX-XXXX
ro.product.name=x10_XXXX-XXXX

7. Press "Menu" and choose save and exit
8. Reboot your Phone
9. Open PC Companion
10. Choose Support Zone
11. Choose Repair (Your phone will be reset and will update with the newest firmware)
12. When done check your settings in de lock screen (menu-back-back-menu-back-menu-menu-back)
You will need to have the phone rooted with the 1-click root.You need a version of root explorer higher than 2.12.2 as this includes the "text editor" mentioned above.

Change the 2 lines in the above "default.prop" to 1234-8465,reboot and then run the Sony update service.
You`ll end up with a debranded Nordic software version with the latest firmware.
Back up everything before you do.I didnt bother as I was going to factory reset anyway for the update.

I have all the required files/apps here if anyone needs them.

The whole process takes less than 5 minutes from start to finish.