I wouldn't suggest deleting the stock ROM..... Since its Verizon you have a locked bootloader and can't flash kernels via safeatrap (safestrap can't flash kernels anyway.) So if you delete stock slot you pretty much delete kernel if I'm right, and you can't Odin it back to stock I don't think because of the bootloader..... So yes make a big backup of the stock. If you want to take the risk of erasing and having a brick you can try it...... Safe strap can only flash touch wiz ROMs because it can't touch the kernel since the bootloader is locked.....
Sent from my Rezound using xda-developers app. CyanogenMod 11. S-off
Verizon HTC One M8
Liquid Smooth 4.4.4 Nightlies and GPE With L S-OFF
Main MP3 Player and WiFi Device
HTC OG Droid Incredible S-OFF: Cyanogenmod 11
iPad First Gen. iOS 5.1.1 Jailbroken with GreenPois0n