as someone who just takes part in these jams, i dont really mind someone else making an edit of their earlier art. the way i understand the purpose of the jam is to motivate people to create new assets.
so as long as you put in effort and you yourself are satisfied that you created a new asset pack, as a participant i think that's fine. it's not like this is a super strict jam, there is no prizes, the only reward here is the art you make.