Anyone know if the expansion adds an in-mission save?
Or has anyone made any kind of patch to do so?

This game be a harsh mistress. Though having no in-mission save works with the gameplay pretty well. You actually have to think about deploying your troops and wotnot, and not resource gathering. You can't really compare it to things like Starcraft or C&C. The total war games might be a better comparison.

At least missions aren't too long so no save isn't that annoying anyway... IM in ninth mission, playing on normal and until present I had only one mision ('No win situation') that I had to replay.

i got fed up with some of the additional objectives that got added.
I'd complete the mission objectives in an apparently unexpected way, and then suddenly they'd throw me out some other mission objective that i couldn't complete with my remaining resources... it was frustrating.
Shame, as other than that, it was a nice game. I gave up on a mission about a downed satellite or something i think...

That one took me a few times.
Deployable AA are handy.

From what I recall from back when I played this on Sierra Bestsellers, there is no in-mission save function and there are no unofficial patches to do so either.

Yes, there's no in-mission save in Ground Control 1. There is on Ground Control 2, however.