Szerintem ne keress túl bonyolult megoldásokat. :)
$ ls -l
total 2
lrwxr-xr-x 1 bra wheel 3 Apr 3 21:58 cur -> old
drwxr-xr-x 2 bra wheel 2 Apr 3 21:58 new
drwxr-xr-x 2 bra wheel 2 Apr 3 21:58 old
$ ln -s new tmp
$ mv -h tmp cur
$ ls -l
total 2
lrwxr-xr-x 1 bra wheel 3 Apr 3 22:00 cur -> new
drwxr-xr-x 2 bra wheel 2 Apr 3 21:58 new
drwxr-xr-x 2 bra wheel 2 Apr 3 21:58 old