On question Jim Winstead told me that APPENDEDNIG to FTP files isn?t possilbe, because it?s not yet implemented, although APPEND is available as a FTP command.
APPENDING to an existing file would be a great enhancement, because one does not have to cache the whole file, appending stuff to the cache, deleting the old file and then creating it once again.

So a function (or mode) would be great, that supports appending content at the preferred position to a file.