If I received that in a letter, I'd still err on the side of sticking close to canon content and tone.

I still wouldn't include extremely controversial content unless I got a specific go ahead. (Eg "I have no DNWs, and I'm fine with character death, torture, and noncon.")

I definitely would use common sense about sensitive subjects, and not take this as a challenge to write the darkest fic I could. (Eg "Character A tries to save Character B from dying of COVID!")