As the EF single player source code was released (a long time ago now), would it be possible (without having to make all your own code) to restore the network code to the elite force single player exe? Since it's quake 3 engine, obviously the network code was removed, so I'm wondering whether it could be restored.

If any programmers are around, any insight?

do i understand you correctly that you want to utilise the SP stuff in MP?

Basically, multiple players using the SP client.

Not applicable without massive rewrites.
Someone once started a coop mod (can't remember who) but they stopped.  The MP network code is incompatable with the SP stuff.  Plus you'd have to pass ALOT more data when doing a Co-Op.

Yes, thesnerd stopped. He was at a disadvantage though. The SP source code was not released back then. He had to write his own icarus handler.

The networking code is integral part of the engine itself. Only the sourcecode for the virtual machines has been released until now, not to the engine itself. So no, it is not possible. At least not for as long as Raven does not release the source code to the engine itself. In theory, they could even do so, the quake3 engine code has been released as well.