Most Games and Mods rely very heavily on knowing what platform they are targeting. This makes it very difficult to port complex modifications between platform versions of the game even if they seem to be similar on the outside. Simply re-targeting the XML will not aid in handling numerous internal function calls that will not be recognized outside the target platform.
There are two 'solutions' I can think of.
The first is to recompile or to make a similar mod using Mac versions of the modification studio targeting a mac version of the game.
The second is more of a cheat but is far easier. With the power of modern computers it is possible to emulate more modern OS's inside each other. Host a VM on your Mac and emulate a windows OS, install grid 2 and load up all your windows mods.
I use Oracle's free VM to do this for numerous games.
Link : https://www.virtualbox.org/
So my solution is not to run it on Mac OS. . .or to make a different mod. Neither of which actually solves your issue. Sadly I do not know of any quick workaround for cross platform software, and if we find one we will be very rich.