ORIGINAL: Korps
If you feel it needs it then put it in - if it flies better then leave it - if it flies worst then just take it out again.
That's my thinking. If they used a GP adjustable mount you can even slide the mount/engine over to get the shaft centered again. Engine thrust angle is something I decide on with in flight testing. I add or remove it as needed. For testing I just use washers but when I hit the magic spot I make a hardwood shim when I get home.