Emod is a very small mod which essentially enables you to call compile a file before any other mod loads. If you open A3Launcher (http://www.a3launcher.com)and download Emod (0.2) and wait a second for that to download. Then press settings (in the top right) and press "open mod folder", this will take you to your Arma 3 directory. Go into Emod02 and then look at the Readme.txt (I will summarize below).
Simply load this mod after epoch:
-mod=@Epoch;@EpochHive;@Emod
(This is the instruction for loading the mod in the arma launch parameters)
In your description.ext (mission file) add the following:
class CfgEmod {
override = 1; // Set to 1 to enable the override
file = "maca134\precompile.sqf"; // path to the file to be call compile'd before Epoch's compiles
};
(The directory above can be changed to wherever your precompile will be located, it is essentially an sqf file that will define variables and run anything you would like to run before Epoch)
And you're done, its as simple as that. Then add whatever you would like to add in there (a quick example below).