Originally Posted by shredfast
I'd like to have a way out of it. I've been reading up on the Android Recovery Mode: Wipe Data/factory reset.
This is oversimplified, but the files on your phone are more or less organized like this -
1. User settings, installed apps (data partition) - this is what a factory data reset would erase.
2. System files (most of them) - these read only files don't normally change unless you get an OTA firmware update. If you accidentally delete or somehow corrupt system files, you can reinstall the firmware to fix these. A custom ROM (if your bootloader was unlocked) would replace the files here.
3. Cache. These are temporary files. Some problems can be fixed by deleting these. If deleted, your phone will rebuild the cache when it boots.
4. SDcard. Built in, internal storage space for user files, downloads, etc. If you have a physical SD card, that is seperate and referred to as the external or secondary SD card.
5. Other stuff e.g. the bootloader, modem, etc.
A 100% backup is often referred to as a "Nandroid". Meaning that you backup the entire memory (NAND). You can only do that properly with a custom recovery like TWRP or CWM. The next closest thing would be an app like Titanium Pro.
The system data reset will only default the user settings (data partition). It won't remove most user files (internal SD card) or touch the read only system files (system partition).
I don't know what your second question really pertains to. You should have described it fully, rather than try to get us to replicate your Google search. I'll just say that it's highly unlikely that anyone will figure out how to unlock the Verizon bootloader anytime soon.
Verizon has an unlocked Developer model phone, but it is handicapped by poor firmware updates. If you want the advantages of an unlocked bootloader, change carriers. Most carriers do not lock the S5 bootloader. Just ATT, Verizon and a few US CDMA carriers.
Because your bootloader is locked, you can't use a real custom kernel or recovery. But they can be emulated with Safestrap.