Great question! That's a tricky one, because there is a really fine line between offering up what you think is a cool new idea, versus the director feeling like you aren't delivering what was asked.
The best tactic to take would be to pitch your idea to the Director (or maybe first to your Lead Animator or Animation Supervisor, depending on your hierarchy at work) to see if other people can get excited about the idea. Most studios do not want to think that you're animating Idea A only to find out you've spent all day working on your own Idea B -- that could land you in some hot water, so at least get permission to flesh out your ideas before spending any company time on them.
If your supervisors like the idea, or if you're working directly with a client but maybe don't have the opportunity to pitch your idea before the Director will be expecting to see the work at least blocked in, then my advice would be to do two versions. I know it's extra work, but if you keep them both rough, you can often find time to put together a version that the client asked for as well as your own proposal of how you envision the scene.
What you DON'T want to do is ignore the Director's request completely and instead only work on your own version. There's a chance they might love it, and you'll be hailed as a hero, but there is an equally great chance that they might be angry. I've seen this myself, and Directors are never happy when they start to feel like the crew is making their own version of the movie behind his or her back.
So, I guess my advice is to put together the coolest proposal you have time to do, but to have the "real" version of the scene in your back pocket in case the Director isn't on board with your idea. A little insurance never hurt, and even if they don't like your proposal, they'll probably really appreciate the extra effort, and may even start to see you and your studio as more of a creative partner they can look to for other ideas!