Command palette items are created by ".sublime-commands" files in various locations in ".../Packages/". It is possible to add items to the palette by adding a ".sublime-commands" file to ".../Packages/User/" directory. However the commands with the same "caption" appear as duplicate in the command palette. It would have been more sublime-like behaviour if the user-defined command palette item would override those of packages and default. Or at least there could have been an override switch.
Customer support service by UserEcho