OpenRA

Then it seems that I have a problem, without changing anything else or making new folder, from old c&c mod I changed cost value of mammoth tank and it haven't changed (of course I've saved). What can make such an error?
Edit: works for playtest but not for normal version

Is there any modding guide for current version? And how is it even working? I couldn't even change rules, I made tweaks and stuff even like cost decrease but it wasn't really in the game. Can somebody explain how exacly openra reads stuff?