Downloads in Dock custom icon won't stick

If you want to change a folder icon or system icon You need to change the the icon in the following path

/System/Library/CoreServices/CoreTypes.bundle/Contents/Resources

If you want to change the icon of an application, go into your applications folder through the finder window, right click on the application icon and click show package contents. Click contents, resources and change the application icon in that folder with your chosen icon image.

The chosen image must be in icns format. If you have a png file or any other icon file you can use an app to convert the image to .icns When you've changed the icon go into terminal, type Killall Dock and hit the return key. Then type Killall Finder and hit the return key again. Quit Terminal, Restart the mac and changes should take effect. It may take a few reboots in some cases for the change to show up under mavericks.

 

It can hold a custom icon, I've done it myself using the method posted above and it works. I'm not sure why yours isn't holding but if you follow the steps I put in my previous post, this will fix your issue.