Normally to change a symlink target one will first unlink the file and then re-creating the symlink with the new target path. However it will be assigned a new inode number.
Maybe there is a private Mac api with an update_target_for_symlink() function, so the inode can stay the same?
In case you wonder what I need it for.. a file manager. I doubt that this is possible at all. Anyways thats what makes it interesting.
A link is an additional name associated with the inode. So there is no possibility to retarget a link since the link is not a unique object targeting a file. It is more a secondary name of a file.
Thats why you have to unlink it first (delete the name associated with the file) and then create a new link (add a additional name) to the new file.
The Inode of the link does not belong to the link, it belongs to the file. A file consists of list of names("links"), an identifier (inode) and a bunch of data blocks containing the file contents.
A symlink should be possible to rename, cause it only refers to the text name of a file.
From manual: There are nine system calls that do not follow links, and which operate on the symbolic link itself. They are: lchflags(2), lchmod(2), lchown(2), lstat(2), lutimes(2), readlink(2), rename(2), rmdir(2), and unlink(2).
Upon looking closer, ln -sf seems to do what you want.
The first column is the inode number. Note it doesn't change:
$ ln -s foo bar
$ ls -li bar
16503 lrwxrwxrwx 1 golemon golemon 3 2010-08-21 12:29 bar -> foo
$ ln -sf buz bar
$ ls -li bar
16503 lrwxrwxrwx 1 golemon golemon 3 2010-08-21 12:29 bar -> buz
It looks like ln-sf uses simply unlink() and symlink() to accomplish this:
$ strace ln -sf quux bar
<snip>
symlink("quux", "bar") = -1 EEXIST (File exists)
unlink("bar") = 0
symlink("quux", "bar") = 0
$ ls -li bar
16503 lrwxrwxrwx 1 golemon golemon 4 2010-08-21 12:31 bar -> quux