[tshering]

You can get rid of the power-on picture by editing the affiliate in .kobo\affiliate.conf (Other affiliates, e.g. kobo, do not show a power-on picture). If you really want to replace the picture, this would be more complicated, since the image is not available as a file but is rather included in one of the binary files (nickel).
As for your actual question, please search for the thread that explains how to replace the internal sd by a larger one. Alternatively, you could create the backup image of the sd also by using netcat (you can find information on this also here in the developer's corner.)