What's the best way to do a bulk namespace rename on a large c# application?
Right click on your current namespace and select Refactor -> Rename and change the name in the pop up that comes up after a while. Enter your new name and click ok.
If you have multiple depths to your namespace, then Visual Studio won't let you type a dot. However, if you copy and paste a dot, despite a warning, it will do the business.
To completely change to the new name, you will likely need to make additional changes manually. You can find where by performing a project search (ctrl+shift+f) for other references to the name in the Project, Solution, or other supporting files from a separate text editor like VS Code. Finally, folders may need to be changed manually as well.
ReSharper. Get version 5.1 from JetBrains for free for 30 days (more than enough time to do your renaming). Put the cursor on the namespace you want to change and hit Ctrl-R twice (ReSharper Rename). It'll work with a namespace any number of levels deep, and converts any usage of that namespace to the new one. However, you will have to change every unique namespace in your solution (unless you just go with Find/Replace)
Visual Studio 2019 Community Edition supports this as described here. It works for any hierarchy (with dots, root namespace changes etc) and correctly updates all dependencies.
Place your cursor in the class name
Press Ctrl+. to trigger the Quick Actions and Refactorings menu
Select Move to namespace
In the dialog box that opens, select the target namespace you'd like to move the type to
