1. You must be seeing a folder \ExtROM here which has few cabs and tsk files. Place this folder on \Storage Card of your device.
2. You can add the files which you wish to autoinstall after hard reset to this folder. But, dont forget to modify the \Storage Card\ExtROM\Config.txt accordingly.
3. Mark all cab files as read only.
You now have the Extended ROM back on your device but on the storage card this time.... Enjoy.
4. Install PPCPimbackup utility by Dotfred on your existing ROM and backup your SMS using that. And then flash the new ROM.The utility is available in this folder also.
I have two questions in upgrading your ROM and the ExtROM
1) How to do this step ->Mark all cab files as read only
2) Can i flash the ROM first, the copy all ExtROM files to the SD card, and then do a Hardreset -> i have done this but seems not work.