Some guillotines have protection, like the one I'm using:
https://www.amazon.de/Dahle-Hebel-Schne ... =dahle+561
However it is only rated up to 35 sheets. Bigger ones are more expensive, although you can get cheap used ones.
I use a heat gun to heat the glue in the bookspine and then gently remove the pages. Afterwards I trim off the uneven, glued edges with the guillotine. This leaves the cover intact. If you have poor sight this might not be the best way to do it, since you can burn yourself with the heatgun if you're not careful. Other downsides to this method are:
1. Melted glue gets on some of the pages as you are removing them. If there is a lot of glue it can become a bit of a mess and you might need to reheat the glue to wipe it off the pages.
2. Takes more time than just chopping off the spine.
3. Edges of pages can be damaged when you try to remove them
4. Cover plastic can become loose if you heat it too much
I've heard of people heating the book in a microwave and then removing the pages, but I like to keep my books and food separate.
