A backup is the single most useful precaution before testing a mod that can intentionally alter a world. The goal is not just to copy the save once, but to make sure you know where the clean copy is and that it stays outside the active profile.
Close Minecraft before copying
Exit the game so region files are not changing while you make the backup. Then copy the entire world folder rather than only selected files.
Store the backup outside the active profile
Use a separate folder so a launcher reset, profile deletion or mod event cannot affect the backup copy.
Name backups clearly
Include the date and a short label such as “before-broken-script-test” so you can tell clean and modified versions apart.
Test restore confidence
Before a long session, confirm you know how to place a copied world back into the saves directory. A backup is most valuable when the restore process is familiar.