Think ur ext rom will be blank this way
but it's not true. I've done that and your Extended ROM is not deleted
1. You chose the ROM you want to use it (and you use xda3nbftool.exe if the ROM comes from another operator than yours)
2. Before launching the ROM installer "BaUpgradeUt.exe", you remove the Extended ROM package which is call "ms_.nbf"
and you update your ROM normally
Only the CE ROM and Radio will be upgraded. Your Blue Angel will keep your old Extended ROM.
If the ROM you have chosen comes in a package like BA_WWE_BelDT_12200_557_10602_SHIP.exe, you can open the ifile with WinRAR to extract its contents.
Simple solutions for a simple world!