What I have done now, set my main Project to Paid, have the free version be as a Demo free in the project and future DLC's I will put in separate projects where I can use the Sale function, like if they have bought the Paid version they get the DLC 50% off. That's one system I really like on itch. They did a good Sales system.
Exactly. Where you can set another game as a condition, for them to have in their Library to be able to get that promotion. But, only those eligible will see the promotion, which is a point that is annoying. Would be great if it's public so everyone can see it and then maybe Increase your sales of both the game and the dlc.