Paul, I guess we have changed far less to most of our courses since the war than the more affluent US. Moortown has had changes (certainly for the poorer) forced on it by housing being built on what was previously Moor Allerton and Sand Moor courses. Interestingly, I don't think much damage is being done to the majority of courses by the performance explosion because pros rarely play classical courses on their tours. They do, obviously for the Open and, for that, regional qualifying is often played on courses of quite modest length (Beau Desert, Stockport, Prestbury, for instance are all about 6,300 yards). These courses are compact and could not really be lengthened significantly.
Quite a few changes have been made because of the public. Lindrick had to abandon a hole because of its proximity to a busy main road. Sandiway lost two or three holes to a new road back in the 1960s and the replacement holes do not seem to have much in common with the rest of the course (Ray/Colt), although the 3rd is a very fine mid-length par-3. The building of the M60 around Manchester apparently ruined Didsbury, a MacKenzie course. It now has a number of very awkward holes squeezed into the very corners of its limited acreage and a horrid, long footbraidge crossing of the motorway to a distant part of the course beside a rubbish tip. Perhaps the worst vandalism was the digging up of a considerable part of another MacKenzie course, Hazel Grove, because of the threat of a large road being built over part of the course. This threat was present even before the Second World War. Some time in the late 80s or early 90s the relevant bit of land was compulsorily purchased by the relevant authority, including the old 17th, apparently one of MacKenzie's finest par 3s. The road was officially cancelled some time after 2000 and the club tried to buy back what was left of the compulsorily-purchased land (including the old 17th). Some of the land had by then been sold for housing and could not be reclaimed, but the club was refused the chance to buy even the former 17th. You drive in through the hole on your way up to the club. Ohhhhhhh!
Does anyone remember Birkdale before the old short 17th was eliminated and the new 12th (rather a good hole, I always think) inserted? There is a lengthened 17th now, with a new green farther on. I haven't seen it, but it could be very good if it utilises for its green site the tumbling ground up by the 18th tee. As you say, Royal Liverpool has been substantially changed in several stages since the war. I noted the expert opinions of many eminent GCAers at the Buda Cup, most of whom felt that the most recent new holes are not stylistically similar to the rest of the course. This may be true, but I have always felt that, with the exception of the old 10th and 12th, there was never anything stylistically consistent about the previous layout. Each hole was very different - certainly no harm in that.
Changes were made to Fulford when the York By-Pass was built. Unfortunately I didn't know the course before that and older members who remembered it say that a great deal was lost. Certainly the holes on the far side of the A64 have always appealed to me far more than those nearer the clubhouse.