In Free Ride, there are pictures in the Don's office and the meeting room that you can activate to change weather and time of day.
I found 11 of these in the base and found 9 of the 11 locations, completing 7 of the challenges. The challenges are pretty much all copies of challenges from Free Ride Extreme, but fewer of them give you car unlocks. Some give outfits and/or weapon skins.
I put another 6 hours into the game, mostly in Free Ride, getting some more achievements and completing some of the challenges, but I think I am done with it unless at some point I get the urge to go back to get the Classic Mode achievement, which is a distinct possibility. I did do the race mission again to get a related secret achievement. Spoiler: