For logo. Ok, size constraints and need for executable is acceptable, although quite limiting. As you can see curent logo ocupies the complete required space it fits the spirit of current design and ideas of original creator of design.
I don't understand the need for wild compo.
If the result is not C64 executable, obviously it can't be submitted here. You will have to organize the compo outside the CSDB. Maybe the compo should be about making a new "skin/color/css scheme" for CSDB, but then it wouldn't be a C64 compo at all either. Of course, it's intriguing idea to have new skin for CSDB (I think Jailbird was succesfully playing with the idea in past) but there is technical limitation to that as site has many features and areas and it's html layout is probably tightly intertwined with code and not having enough unique identifiers to aim designers touches precisely enough to avoid breaking changes somewhere else (I'm just guessing her e though)
Another problem is, that backdrop was initially meant like soft touch in the design, it wasn't meant to be prominent part of the site, that's why it's so dark. With C64 palette it will scream in the header of this site and it will probably collide with current color scheme (buttons color).
For reference for others, you are talking about replacing of those two files: https://csdb.dk/gfx/csdb_topgfx.jpg https://csdb.dk/gfx/csdb-logo.gif