What does Restyle annotations do?
Restyle annotations changes the highlighting style that is applied to all notes/highlights that currently use the selected style ("Blue Thick" in your example).
When you click it, a popup menu of all your highlighting styles will appear, allowing you to pick the new style to use.
It's the same as finding each highlight that uses the "Blue Thick" style across your documents, clicking the note indicator icon for each one, then choosing a new style.
So its basically a search and replace , right?
Thanks Bradley
EDIT: that is really cool (i just recently updated to 4.5a from 4.3)