I'm running SoC through Wine on my mac. I'd like to eventually install some mods, but I need some help. I read that in order for mods to work, you have to edit the fsgame.ltx file. Problem is I can't open it. I don't know how to open it on textedit to perform the necessary edit. And then even once that's done, I wonder if I'll be able to properly drag-and-drop and/or run all the files and folders of various mods. Anybody done this before on a mac who can help me out?

You should be able to right-click, Open With and manually browse to TextEdit. Mod files should work just the same as the game itself (since they're in the same location); most mods will include the gamedata folder all ready to go so you can just drag that folder into the main installation folder alongside the normal game files.

Some mods include special EXE/DLL files so you might need to do some extra tinkering to get those working under Wine.

I can't do anything to it through Wine's file manager, and I can't figure out how to access my Wine files through Finder.

Show Package Contents.

Alternatively, you can use terminal and edit the file with vi. ;)