Hi! Sorry I'm so late to reply to this. Sadly, I have no secret to preserving mine. I consider part of the challenge of pumpkin design is accepting its very brief existence. That being said, acrylic fixative, or a bleach soak will keep the details crisper for a few days if you're working in fine detail.
This is such a beautiful design! And the carving is so well done. This is the first year I've tried to carve a fancy pumpkin and it was quite difficult. What tools did you use for this? I'd love some tips and pointers if you don't mind divulging your secrets.
actually my only tools were a washable marker, a standard pumpkin knife like from those kits you can get anywhere, and an Xacto blade. The best trick is just to work it out in your head first, where you want to have lights darks and mid tones, and experiment with how far you cut into the meat, as it will vary how much light gets through.