Yaarel
🇮🇱 🇺🇦 He-Mage
But if your own content modifies the CC Open Content, it must also be Open Content too.That would IMO only apply to CC licenses that include SA (share alike), e.g. CC-BY-SA. If you license your content as CC-BY (credit source), then there is no need to open up your own content as well.
Still, it would require a bit of extra work since you need to extract the shared content and make sure you don't accidentally share things you consider product identity.
For example, say, you create a brand new game from scratch. You write up an SRD for your game and give it to the CC license for others to use.
That CC actually discourages other creators from creating products for your game. Because while they modify aspects of your game, they can make money from their modifying products − but cannot protect their own intellectual property, since it would necessarily become CC Open Content.