It happened fairly often in the old days. Walter Travis built a course for Milwaukee Country Club, only to have Hugh Alison come along and totally change it within 5-10 years.
It's rarer nowadays, because so much of marketing is predicated on the architect's name, so when it does happen today, it's bound to be more catty. The most visible instance was when Tom Fazio was hired to redesign one of Greg Norman's courses in Arizona before it even opened. But I know of a couple other instances like your number (1) or (2) where the original designer was asked to change something, refused, and another architect was brought in to make the change.
And, of course, there are tons and tons of courses where some architect has done a remodeling, only to have someone come in 5-10 years later and do another. It's funny when both of them are labeled "restorations".
In general, I think clients owe it to an architect to talk to him first, before bringing on someone else to make changes. I have made a couple of changes to my own courses that I didn't feel were necessary, but decided it would be better to do them myself than to have someone else in there messing with them.