Is it possible to move a manual snapshot from one instance to another

If your goal is to minimize downtime, you might consider creating a new instance from your snapshot, then pointing your static IP to the new instance once you've verified the new instance is working as expected. When you're satisfied the new code hasn't caused a regression you can delete the old instance and will only be charged for the time you were using both instances.

This assumes that you've configured a domain to point to a static IP, and that static IP points to an instance. This is a good practice because the public IP of an instance can change when you stop/start the instance.