Oh my god, thanks! Saved me some time and maybe some money there

There's no way to change it, it's automatic. There is a registry key for your game installation location but the mods folder location cannot be changed unless there was a way to change the location of your entire AppData folder through Windows.

Well that sucks. I guess I could just move maps back and forth from a different drive and just keep the maps I'm currently playing on the C: drive...

I don't know if this is the BEST option, but if all you've done to your WAW root folder is install mods  (basically you aren't a mapper), it may be easiest to just copy/paste your WAW mods folder onto your desktop, delete the WAW root folder, and uninstall the game, then re-install it on a different hard drive, and place the mods back there in that root folder. considering the game is fairly small, it shouldn't take too long

I already have the game installed on a different drive, but the game stores all the mods in C:\Users\<USER>\AppData\Local\Activision\CoDWaW\mods

My SSD C: drive is full and WaW mods are one of the things that are taking up the most space. Is there a way to set a new mod directory on another drive? And I don't want to delete mods either, but if it's the only option I'll have to do that.