My advice would be to use TiddlerNotesPlugin:
http://lewcid.org/2007/10/26/new-tiddlernotesplugin/
http://tw.lewcid.org/#TiddlerNotesPlugin
Then you could use the DeleteAllTagged bookmarklet to remove all
tiddlers tagged with "notes" (or whatever tag you have specified for
your TiddlerNotes):
http://lewcid.org/tiddlywiki-bookmarklets/
However, I agree with Nicolas that this might be a problem if you've
already written a lot of notes that are not easy to distinguish.
Also, the ForEachTiddler macro call we've composed for your highlights*
might be adapted (with some additional effort), depending on what your
content looks like.
-- F.