It will upgrade your hboot to 1.58, but not change your S-OFF status. If you want an hboot other than 1.58 you can use this post to flash one after you install the new firmware.So that will upgrade my HBoot? Do I need to do anyhting special to protect my unlocked-device status?
Whether or not the bootloader is unlocked doesn't really matter as long as you are S-OFF. I assumed that you are since this thread is intended only for S-OFF users.
ramjet73