Adhesives can sometimes be removed. Do not use an extremely sharp knife as it's too easy to slice off the glossy surface of the paper. This falls into the category of stuff that shouldn't be done to a rare or valuable book. Bookplates Do not use Goo Gone or lighter fluid to attempt to remove a bookplate. It won't work.
Bookplates usually have a water soluble paste rather than glue.
Only water will remove a bookplate, and it's a very tricky procedure. Personally, I just leave bookplates where they are, but if you are determined to try, then take some kind of absorbent paper, preferably blotting paper, and cut it down to slightly smaller than the bookplate. Now place a sheet of wax paper over the whole page, close the book, and place a weight on it to keep it tightly shut. Leave it alone for a minimum of half an hour before you even look. You should be able to very carefully lift the bookplate up from the edges bit by bit.