FTP'ing files to server, then renaming them.

[Alexander V. Lukyanov]

Is there a way within LFTP to either send up a number of files up to an FTP server, then change their extension (from say ".temp") to something else like ".data"

Please try development snapshot http://lftp.yar.ru/ftp/devel/lftp-4.5.5.20140918.tar.gz
It has support for transfers via a temporary file, use "set xfer:use-temp-file yes".
I have used .in. prefix, like an old mirror program did.