Templates to replace Unity's default template for new C# scripts.
Under the following path:
C:\Program Files\Unity\Hub\Editor"Editor version folder"\Editor\Data\Resources\ScriptTemplates\
You will find a file named:
81-C# Script-NewBehaviourScript.cs.txt
Replace the content of this file with the content of any file under Templates and save.
Now, the standard Monobehaviour script template is changed when creating new scripts.
When using the NamespaceTemplate, the script ScriptTemplateKeywordReplacer.cs will exchange #PROJECTNAME# for the project's name, simulating the act of moving the class to a namespace.