The
Hyades Rim mod lets you save mid-mission, and while that's a good story, it seems to be a bit different than what you're looking for.
Don't think it does anymore. I recall when I looked at the last download page, it either stated or seemed to imply (I forget which) that had been taken out as well, for the same reasons as BEX, BTA3062 and RogueTech did.
I've started playing the game again after a 2-year hiatus. I downloaded/installed 3062 Advanced and... what a wake-up-call! Even with easier settings I find myself getting B!#@H-Slapped almost every mission. My biggest problem is time; I don't have a lot of it so I have to rush to get missions done because there's no save function mid-mission. Is there a Mod to help with this, or a Mod/Mods that add the appropriate tech at the proper time as I advance in the vanilla game?
I'm afraid that you're are, as they say, pretty much fragged on this point.
All the big mods ended up having to disable in-mission saving, because the version of Unity HBS uses appears to be frankly crap, so it pretty much never works properly even if you can try it. There are ways to toggle it back on, but the problem is apparently that loading an in-mission save just doesn't WORK properly with mods on. Crashing out and errors are that frequent.
And, as PDX and HBS have stopped support... Nothing is going to get done about it. Likeley even if you could get into the hard-coding, to fix it, you'd probably have to update the Unity version. (Which I understand from Brightrock Games, who actually did on War for the Overworld - putting PDX to shame, they cant even fix their OWN published games, Imperator - is a difficult job in an of itself).
So it comes down to basically Vanilla-with-saves or Mods-without-saves, pretty much, I fear.