Installing Google Now on Verizon Galaxy S3 (SCH-I535)
If you follow the method found in the LifeHacker article, you would indeed need to root your phone, which would mean that you wouldn't be able to receive OTA updates, unless you were to later un-root your phone, going back to the stock firmware (ROM).

You wouldn't necessarily lose your current settings, but you would have trouble upgrading to Jelly Bean via an OTA upgrade unless you un-rooted, as mentioned above.

I'm sure you would have to unlock your bootloader as well, prior to rooting, although I'm not really familiar with your particular model of phone.