Modifications were done in production, apparently not to already completed aircraft, but it's still about 90% a DC10 freighter. (There have been suggestions about pulling some retired DC's out of mothballs and doing it over again)
"Derivitave" certainly but we're parsing.
I'm not trying to parse or be argumentative at all. Just making the point that the are tankers based on the DC-10 design, but were built for the USAF. They weren't old, used DC-10 that were converted to tankers. Call that a modified DC-10 if you like.
All info based a little personal experience....