If you’re not copying setting, characters or story then you’re not copying everything. Those are also part of the recipe that makes the game work, through things like level design, narrative design, and game feel.

Copying critically means not just copying blindly but understanding how things work and why they were designed that way to begin with. You talk about wanting to make changes, but do you know how they would affect all the other parts of the design?

It’s very common for new game designers to dive into making changes without a full understanding of what they’re even trying to solve, let alone the knock on effects of their proposed solutions.