Snow Leopard is full of little surprises.

Last night, I posted an icon of Canada’s first ever mail stamp as a mail.app icon, and simply assumed that the tried and true way of changing it through the Inspectors still works. It doesn’t.

As Chocky helpfully points out in the comments (thanks!), the permissions of the core apps in Snow Leopard have been tightened so that you can’t by default copy and paste over the image of the icon in Apple Mail’s Inspector pane anymore.

However, all is not lost. I first tried brute force. I copied over the icon in Mail’s application package. That works fine, but is a little involved.

Fortunately, a few, simple additional steps can make the old method work again.

First, close Mail. Find Mail in the Applications folder, and press ⌘-I (Command + i) to bring up the Inspector pane.

Step One: Unlock it by clicking on the padlock in the bottom righthand corner of the pane. You will need to authenticate.

Step Two: Change the permissions listed for “everyone” from “Read only” “to Read & write”.

Step Three: Proceed as normal under the old method. Copy (⌘-C) the image of the icon that you want to use from the top lefthand corner of its Inspector, Select the Mail icon in its Inspector and paste (⌘-V) the new image over.

Step Four: Remember to change the permissions back to what they were.

All done! I’ve tried this three times now, and it’s worked every time. At the end of the process you have the new hand-crafted icon on Snow Leopard’s Mail:

If, on second thoughts, the new icon looks terrible, it’s easy to change it back again.