I'm on my last tray and am thrilled with my smile! Can I refuse refinements?

This is a discussion you will have to have with your dentist.  It's great that you are pleased with your smile.  Your dentist is viewing your case from dental perspective and may notice minor improvements that you may not notice. Talk to your dentist and discuss what it is that will be accomplished with the refinements.  This will give you a better understanding and may help you make up your mind.  Hope this helps.  Good Luck!

Congratulations on your new smile! I would recommend asking your dentist why the refinements are needed. If the refinement is for aesthetic reasons you can take a pass. If it is needed to make a correction in your bite it is in your best interest to complete the treatment.
Good Luck

Of course you can refuse refinements. What's the reason that your dentist wants you to get refinements? that's more important. If it's a serious issue, you might regret it later. If it's just a matter of mild cosmetic concern, then you just need to sign a form /consent that you're happy w/ the result & move on to retainers.
 Enjoy your Smile!