I wrote: A bonsai is a living and evolving work of art. It may be kept
approximately the same size for years. The grower may choose a different front,
may let it grow larger, or may cut it back & make it smaller, then repot it in
a different pot, just as a curator may sometimes put a painting in a different
frame.

You wrote: Whenever the owner of a work of art wants to change something
about it, for example to fit it into a frame or close spot, he is likely to get
sued by the artist, who regards this as defamation of the work and an
infringement of copyright.

This question is discussed in bonsai circles all the time. In general, when you
buy an ordinary commercial bonsai, especially an anonymous one, it is now
yours, and you are free to restyle it as you please. In the case of a very old
masterpiece bonsai, the current owner usually tries to maintain the original
style as intended by the original artist. But since a tree is alive, there are
problems. Sometimes a major branch dies, or a couple of trees in a group die.
Sometimes the proportions change as the tree ages, even if the overall size is
kept the same. In these cases, a big expert is called in for a complete
makeover, which is often published in a magazine.
One interesting situation is the Lars Anderson bonsai collection at the Arnold
Arboretum. They were brought to this country by the embassador to Japan around
1905, and were created in the bonsai styles of that time. Let me tell you, I
have seen them, and by today's standards, they are BORING. But as the earliest
examples of bonsai in this country, they have great significance. The arboretum
people have maintained them in their original styles as much as possible, but
in some cases, they had to completely restyle them for the health of the tree.
Iris,
Central NY, Zone 5a, Sunset Zone 40
"If we see light at the end of the tunnel, It's the light of the oncoming
train."
Robert Lowell (1917-1977)