The rules say that the reuse of code and previously made assets are ok. https://itch.io/jam/go-godot-jam-2
It sounds like from what you are describing that would not be outside the rules. Though i guess there might be some wiggle room depending on how much of the game was complete. I imagine a simple palette swap might not be acceptable.
That said grain of salt with everything I'm saying since I'm just a participant.