Yes the main differences in Recharged is the maps and the graphics, as well as some other functions such as the level editor and the flight recording feature.
The level editor will automatically save the levels in the folder location where you have put the app itself.
My guess is that you do not have write permissions in that folder location.
A fix would be to enable the write permissions to that folder, I'm not sure how to do that since I'm not a Mac user myself, maybe you can find some useful info in a video such as this one:
https://www.youtube.com/watch?v=7mx2XOFBp8M&vl=en
If that is not possible, maybe you can put the Freerider app in another folder where you are cerain that you have write permissions.