How can I change an application icon in Mac OS X?

"Select the application file in Finder.
Open the Info window for that file (File > Get Info, or ⌘I)
Click the icon in that window (a blue border will appear).
Paste in a new icon.

Any image you can open in Preview can be used as an icon: open it in Preview, select it, and copy it. That will put an image on the clipboard that includes a format that can be pasted as an application icon."

"According to macosxhints.com, it seems that in 10.6 the icons for standard Mac OS X applications (or even Apple software in general) might no longer be easily changed, as the application folders are kind of read-only.

One could of course change those access rights, but changing the package contents might break the Code Signing's signature for that application. And if the signature becomes invalid, then applications might no longer be allowed to access the keychain, will no longer be permanently allowed an exception in the firewall if it's known to check its own integrity (known to have caused trouble for configd, mDNSResponder and racoon), or might cause trouble when using software update.

(Above, might indicates that I am not sure. Some quick tests changing the iTunes, Safari and Activity Monitor icons did not break the Code Signing, though for some other, yet unknown reason the firewall might repeatedly ask Do you want the application “iTunes.app” to accept incoming network connections? For more details see If Mac code signing is tampered with, what might fail?)"

"If you're having trouble getting this to work, like me, then I found a solution.

A Firefox update a long time ago brought back the classic icon - I, like many others, use a custom Tails icon (google it, it's really cute!) and I tried to set it back, but it wouldn't have it. Pasting over the icon didn't work.

Just this evening I found the problem - within Firefox.app was an Icon file, but when viewed from Terminal it had an unprintable character on the end. Turns out there was a Windows line-ending in the filename (possibly a bug in the update) that prevented the icon being modified ever since.

Deleting this file allowed me to change the icon again."

I would at least try out a trial version of Panic's CandyBar 3 application. Tuned up for 10.6, I haven't had any problems with it and I changed quite a few icons, including system applications like Finder and System Preferences.

"Just perform this ""Copy -> Paste"":

Open Information Panel of Application (Cmd+I), and Preview of image source.
Copy (Cmd+C) image from Preview and Paste on icon in Information Panel of Application."