If your religious beliefs say that modern medicine is bad then an exception should be made to allow you to opt out and issue instructions that you are not to receive medical intervention when you're not conscious to be able to object.

Those are called living wills. It's a perfectly sensible law that should apply to everyone. You might issue some instructions due to your beliefs like you might use your freedom of assembly due to your beliefs. But in both cases, the law was not made to give a loophole to people with certain beliefs.

If we can suspend the laws at will because people don't believe in them, then they aren't sound laws to begin with and we should repeal them.