How do I change the icon of Emacs installed via Homebrew?

App icons are part of the application and not something easily changed by the user.

Changing the icon will change the data the application hashses over for its signature and so some things will complain the application is corrupt.

Icons can be changed by going to the Application in Finder and then choose Show Package Contents. In the simplest case an icon file will usually be for application X (I think the developer can decide to use another name) X.app/Contents/Resources/X.icns You can then replace that file. However if the application is well written and so complies with Apple's Human Interface Guidelines there will be several icons

Every app must include several sizes of its app icon for display in the Finder, Dock, Launchpad, and elsewhere.

Note that when Homebrew gets an updated version of Emacs and you update it will overwrite the change you made.

I found a way to change Emacs GUI dock and other icons.

1. Download png files from http://emacs.sexy/#icons, or use your own.
2. Take the largest png and convert it to .icns file with an online converter (google)
3. Open Finder, go to Applications, and right click Emacs to Show Package Contents, then navigate to Contents - Resources
4. Replace the Emacs.icns file with your own from #2.
5. HERE's the tricky part - then I had to also do the drag-drop trick.
   • In a NEW Finder window, go to Applications, right click Emacs and click Get Info.
   • Then from the other Finder where you have the new Emacs.icns file, DRAG it to the TOP LEFT small icon in the Get Info window.

No restart required: