Why would you want the scorecard to show it as a par 5, if the scoring record is calling it a par 4? They used one of my courses as an example when talking about this. It's a par 5 on the course's scorecard and is 440 from the back tee, too short to be a 5 under the new guidelines, and when the MGA has events there they'll play it up a bit and call it a par 4 on their card. It's uphill and has a couple of bunkers that encroach the landing area off the tee. The last 90 yards are straight uphill and covered in rough. They said in that case if it was the architects intent that it be played as a par 5 in normal play it could stay a par 5 under the new handicap system.
The wind was strong into me and left to right. With a back left hole location my 3rd shot on this par 4 (yes, 3rd) was 140 yards and playing more like 160 with the temperature around 37 degrees (f). I pured my iron and played just enough left of the hole for the wind to bring it back to the green. Rolled in the 8 footer to save par. Considering my first two shots on the hole, I was elated to save par.
On our last few e-revisions there has been a link that tells you what your index will be under the new calculation. On the first two mine was going down 0.1 and up 0.1 on the last ones. Unless you have some big variation in your 9th and 10th best scores from your best 8 average it shouldn't be a significant change. Some people with an inconsistent scoring pattern will definitely see a change.