Only for launcher pro? not for original launcher?
Where do i find those files that should overwrite?
I only use Launcher Pro; they will probably work in other third party launchers too. The stock launcher is not customisable at all apart from the wallpaper.
For Launcher Pro (other launchers will likely be similar);
For dock shortcut: long press on shortcut > Change icon > Custom Icon > Select the icon from your SD Card using the Gallery app, or other file explorer.
For homescreen shortcut: long press on homescreen > Shortcut > Applications > [APP] > Touch the icon to change is as above, through Gallery or other file explorer.
Hope this helps.