I downloaded it, went into mod settings, and changed them, so the grid was something like 64x999999999999999999. of corse, it didn't work. but then when I disable moar-grid, I cant access the mod settings. deleting and re-downloading It keeps the new settings, so now I'm screwed.

When you go to create a new map you can change the mod settings there. However I'm not sure if they get changed for a current map or not. If for whatever reason you cannot change them there, then you can do the following.

You can delete the "mod-settings.dat" file in the mod directory which on Windows is in %AppData%\Factorio\mods, but this will reset ALL MODS SETTINGS. So if you have more than one mod and set custom settings when creating your map then this will also delete those settings. It will likely also break your current map. When Factorio next launches it will recreate this file with the default settings of ALL mods you have installed.

thanks!