Yes. They can't do an exam on you without your permission - if you say no, they can't hold you down and force you. Make sure that your support person knows how adamant you are about it so they can advocate for you as well if you can't.
At a basic level this is true. No one can examine you without your consent. You can refuse.

What you need to prepare for though is that fact that they won't be happy about it, and will most likely use coercion to get you to agree. This wouldn't be a problem for most strong willed people in a non labouring state but when you're labouring you are very vulnerable. You are also very open to suggestion. So it's important that you have strategies in place with your support people not only to say no, but to deal with the emotional manipulation that will probably be used to undermine you.

Not wanting to scare you, it's just the way it usually works.

It's definitely true that there are many other indicators about where you're at in labour other than an exam, but the sad fact is that 99.9% of obstetricians (and I'd say a reasonable proportion of hospital midwives) are not particularly familiar with them.

I'd suggest that you look into the reasons that they like to do them and then work out a plan to counter.

The other option of course is don't go into the hospital until you're nearly ready to push. They probably won't come near you then.

Good luck.