What do you mean by "Changed progression"?
New missions, changed missions, changed research, weapon balance, etc. New agent types (Olympians, Proteans, Kyberos, Shadowbats), new HWP chassis. A boatload of new countries on the Council to please or fail.
Cult manors are a big game-changer now. There are more generic cultist missions, too. Some interesting lore bits about the four cults getting increasingly desperate as you stomp on them. I think Advent, embassies and alien base keys were still a thing in 1.6? No more.
Ghosts have gotten much more fleshed out. Syndicate has been more or less finished since. UAC was actually developed into something. MiB were changed from their fake UFOs, and there are more of their craft flying around. More M.A.G.M.A. stuff. HSD to be their underwater equivalent.
The reinforcement mechanic which will make you hate crop circles and manors.
More that I'm not recalling offhand.
To sum it up, even if you can get some of the new missions with your old save, you won't experience them in their 'proper' place. The best example is probably the crop circles. If you have heavy armour or power suits, the MiB punks who show up when you dawdle won't even be speedbumps. When you're still in the 'two guys in a car' phase, they will faceroll you so hard you'll
cry IRL.
I wonder if I could copy and paste one of my characters into a new game?
Probably. The only thing that might be an issue is their commendations.
I found the game a slog at the beinning.
It still is.
I had just set up my final base with research and manufacturing bases up and running. Healthy bank balance. A hardcore army of agents
Yeah, I know it's hard to give up your shiny toys.
