No, DO NOT DO THAT. EVER.
Just use MySQL Query Browser to make a new row in the skin table, make a copy of the Basic folder under /usr/pluto/orbiter/skins with the name of your new skin and put that in the Path column of your new row.
This way, you can also make entries in Style and StyleVariation to change text styles, and things like data grid colours.
What I do to make that possible is, in a console:
sudo ln -s /usr/pluto/orbiter/skins /home/skins
sudo chmod ugo+rwx /usr/pluto/orbiter/skins
You then can connect to the \\dcerouter\home share, and put graphics in the skins folder.
With this done, you can select the skin in wizard > orbiters and do a full regen of the orbiter to see your new skin changes. You must do a full regen every time while in development, because this way it ensures you'll see the changes.
As for UI2 considerations, you must understand that in UI2 masked, any alpha channel value below 255 is black, in other words, the alpha channel gets flattened to a GIF-like matte.