Well, you don't have to use the theme that was voted for necessarily, but one of the rating criteria is "Theme Integrity" which is strongly tied to the jam's theme, so not following the voted for theme is unlikely to score you high points in that category.
Will you not play the game if it is payed to download. Sorry, I am kind of new to itch.io I don't know how to change that setting. from paid to not paid. )::