Finder sidebar icon for my folder
Not possible, at least without serious hacking.

OS X supports changing folder and app icons through the "get info" pane (open "get info," click the icon to select it and copy or paste). You can copy an icon from one app or folder and paste it onto another.

However, when I tried this with a folder on my Mac, it did not affect the icon in the sidebar. It looks like the sidebar uses the type of the item to choose the icon, rather than using the icon in the info.