Back up before you mod
Before opening any save editor, close the game and copy the entire BL4 save folder to a separate dated folder. Do not back up only one file unless you already know exactly how the game stores profile, stash and character data. Full-folder backup is slower by a few seconds and saves hours when something goes wrong.
Use offline test saves
Create one throwaway Vault Hunter for testing. If a mod corrupts that character, you lose nothing important. If the mod behaves for several launches, then decide whether it belongs anywhere near your main save.
Online co-op rule
Keep gameplay-changing mods out of public co-op. It is not just etiquette; it protects your own save from weird state mismatches and keeps other players from getting dragged into a setup they did not choose.
What BL4 Tools will and will not link
We will link backup guides, cosmetic-only tools and well-documented offline utilities once they have a public track record. We will not link malware-looking trainers, paid unlockers, or tools that hide what they change.
Useful next pages
If your game is unstable before you mod, fix that first: start with Crash on Startup, Compiling Shaders, and Low FPS / Stuttering.