I believe archive on update is enabled by default, so unless you've turned it off, you should be able to restore to the previous version.
I'm not 100% positive, though.
If this is a reproduceable problem it will most certainly be fixed, although I wouldn't be able to give you a timeframe; the other possibility is that a fresh install would fix it.
My guess is, however, that it's a graphics option that DL now has that DA had that is on by default that is giving your video card problems. This is only a guess, as I have not yet seen what updates, if any, DL has in this new patch.
In any case, it may help to check for a driver update, and if all else fails, obviously enough post your debug.err, found in the \Program Files\Stardock\TotalGaming\GalCiv2 directory (for DL).