- I cannot modify built-in Unity packages.
- Whenever I try to edit a built-in package, the package is automatically rolled back.
Being unable to modify a built-in package occurs because Unity will roll back any changes for built-in packages.
You can modify built-in packages by moving the package that you want to change from Library/PackageCache/ to the Packages/ directory in your project folder  or by customizing the package manifest after you move the package to another location .
(Please use one of the following rather than both)
For example, let’s say you want to edit the ugui (Unity UI) package;
 Move to the Packages folder.
Move the com.unity.ugui package from Library/PackageCache/ to Packages/
|Important: After you move the package, you must remove it from the Library/PackageCache/ folder.
 Use packages from other locations.
If you want to customize the package location, you can move the package to the directory you want and tweak the location for the package on manifest.json.
In the Packages folder, open the manifest.json and edit the ugui location.
(Please replace the link with what you want to use here.)
|Important: After you move the package, you must remove it from theLibrary/PackageCache/ folder.