iPhone 3GS on Modem Firmware 06.15.00. Paid for factory unlock. Will i brick my device?

[suryaclassic]

My iPhone specs {iOS 4.1 (8B117). Carrier 8.0, Model MC137LL, Serial# 869*****3NR, Modem Firmware 06.15.00}

Hi guys,

New on the forum here. Tried to search for this unique situation I am in but could not find any.

I have a iPhone 3GS currently software unlocked on Baseband/Modem Firmware 06.15.00.
A lot of applications that I use are asking me now to update to new iOS 6.0.2 firmware to update the apps itself.
I went ahead and paid for factory unlock and i was advised to restore (its a must... I have to, have to restore) the iPhone to complete the factory unlock process.

Now, to my understanding, if I update the iPhone (which is to the latest iOS 6.0.2), my baseband will change and my iPhone will be bricked right? (Please let me know if that's the case)

What options do I have here?

Do I really have to stay back in the same iOS? Do I have the option of making a custom firmware of iOS 6 and still be able to update my iPhone and still achieve the unlock?

Thanks to all in advance that will help me.

[RochOAR]

Downgrade the baseband in redsn0w. Easy as pie if you follow the prompts. After that you can upgrade to your hearts content with your factory unlock.