You can do this, but you may want to be careful that you don't mess up what you have already entered. What you can do is add California as a state and enter the information as a California resident, even if the system suggests you are a nonresident. (You can override the nonresident selection). You also would want to make sure that any credits for taxes paid to another state don't calculate, and that all of your income is being "reported" to California on this mock return.
As long as you do not pay for the return, you may delete the mock state return, as stated in the FAQ at the end of this answer.
From what I can tell you from experience is that if your income is lower, California has a lower tax rate than Kentucky does. But, at higher incomes, California has the highest tax rate in the country of any state.
And, one more caveat: although you can use this technique to get an idea on what your California tax might be next year (if you've just moved there, for example), you must prepare your filing to the correct state and residency in the state.
But, if you prepare a mock state return and then wish to delete it, here's how: https://ttlc.intuit.com/replies/3301384
**Say "Thanks" by clicking the thumb icon in a post
**Mark the post that answers your question by clicking on "Mark as Best Answer"
