Any modifications to boot or recovery images have to be loki patched to work on the f3's because of the locked bootloader...just the way it is I'm afraid. If you have a cwm custom recovery installed you can restore a nandroid backup if something goes wrong after flashing. The only time you should have to re-flash the firmware is if;
1) for some reason you can't enter recovery mode.
2) forget to make a nandroid backup first.
3) hard brick.
In most cases bootloops, bad flash, mod or script problems, soft-brick, etc., can all be fixed in recovery mode. Only when all else fails do you use the LG Flash Tool.