Here the easy way to change the flex version, thanks to flash.tato for the useful software.

Download the Flex Ver Tool

Connect your phone in p2k mode, then open the FlexVerTool

Write the text you want your phone to display instead of the real flex name.

and then press Scrivi and it will be done, now press Riavvia to restart the phone, and your flex version name should be changed.

thanks to bomber21 for the original guide.