While it's quite a hassle fixing non-compatible mods for mac, if you know how to edit the ini files and interpret the errors thrown up by CC, it's not too hard to fix them.
The majority of the errors are caused, as dogboy mentioned, by the mod makers using \ rather than / in the ini files. While that works under windows, it isn't recognized for paths in MacOS, and so throws up an error.

The error will say something along the lines of "Failed to open included data file Error happened in
ModFolder.rte/Path/To/File.ini at line X!

The line X is fairly important, just in case it's not a \ error, but for slash errors, knowing the file is usually enough.
So what you'd want to do is open up the .ini file in question with TextEdit or something similar, do a search for "\" (Use Command + F) and replace the offending backslashes with forward slashes (/).

Another error you might come across is an incompatible .wav file. I can't remember the error that throws up, either a no such file or a read error or some such. One way I've found to fix those is opening them up with a sound editor (such as Audacity) and re-exporting them.

I think there's one other error I've come across where Windows CC will accept -1 as a value for an infinite Lifetime, while MacOS will give an error. Just changing the -1 to a 0 should fix that one.

As for errors that crash without a message, I've come across a few, but they're harder to troubleshoot. I believe most of them are non-OS specific, so the author is probably going to pick up on them if they're there.

All that said, if there's a mod you want to make compatible and you've tried, and it didn't work, I might be able to take a look at getting it mac-friendly in my spare time.

Hope this helps!

Hmmm that's quite strange, the UNSC mod works fine for me on Mac.