The way I define the terms:
A restoration is putting back the features of a course to how they looked on opening, or some other specific time. This is in spite of the fact that it won’t be played with 1920’s equipment today. Examples: Bel Air, The Valley Club.
A renovation is to rebuild the features of the holes in more or less the same spots they’re in, but cleaned up and with improved drainage etc
Sympathetic restoration is a weasel term - it implies you are going to restore the character of the original course as it would need to be for today’s game - lengthened, bunkers relocated to test scratch players of today, etc. The problem is, you could hire three successive architects to do a sympathetic restoration, and each of them would have a different take on it, and you could just keep spending money that way until the Club was broke.