After long time search, i found Flashing Z550i (CID 49) and did it successfully. My Z550i rocks now. The setps are not so complicated. All you need to have the Firmware files ready which will save you from screwing your phone.
Thanks to SUMEET who has done it acutally in Other forum. All Credits goes to SUMIT. I did not see the positive result here, so i would like to post here.
For the Firmware files, you can visit topsony.com and buy credit for very low prices which will be sufficient to download the required files.
This method is realiable and you can escape from bruteforce method which is a very time consuming process.