What is tone and what are the rules? Succinctly, don’t mess tone up because your script will have the weird vertigo feeling that comes from moral dissonance.
Tone is a simple emotional language you’re already familiar with, unless you’re a psychopath. Or a replicant.
To keep a consistent tone, think “How will this action be judged in this context?”
I failed at tone once by overshooting how I would prove that my roguish love interest was a dog. I wrote a “very funny” scene wherein he hid my girl protagonist, who he had just hit on, from the sudden arrival of his girlfriend, who he then had comically loud sex with.
Why did I think this was NOT a failure? Because it proved what I wanted it to prove. He was a dog. Additionally, his girlfriend was hilariously unlikable, which was bonus comedy.
Why did it fail? Because it grossly overshot the cute tone and theme. It destroyed him as a redeemable bad boy. He was just a giant red flag at that point, and no one who read it wanted the protagonist to end up with him.
Tone is what is acceptable by the audience in a given set of circumstances that you set up. I set up a bad boy and ended up with an asshole.
When you pick your tone, you pick the values that go along with it. Mixing and matching the tone creates logically incoherent characters. If a character transgresses the tone, it must be addressed in the plot as part of their arc.