To the original point, there is a branch called FAF Beta which could be used for any kind of changes without the need to make a mod. You will need to use git however.
@Jip
On the point of EQ, it was a total overhaul balance mod. Every single unit was touched in some way, and many mechanics as well. The only way it could exist was as a mod. It even became a rated mod at some point. I had exotic_retard on the balance team and wanted him to implement things like the mobile factories. It is in no way the balance teams fault that mobile factories only made it into the game many years after they were in EQ. We never stopped anyone from implementing this feature, I even tried to get it made. Maybe you could blame us for not having the technical skills to do it. Should we have just let Ithilis balance the whole game himself? That's what having no bureaucracy would mean I guess. In the beginning it was a dictatorship with no bureaucracy, and we got engy mod and T3 MAA which moved FAF away from FA in a big way.
It's silly to characterise the balance team as some group dedicated to balancing only for the top 50 players and the benevolent game team is out here trying to make the game fun for all. You have no greater mandate from the players than the balance team does. Everyone who works on the game wants their stuff to get in. Someone has to be able to say no, especially to game content. Someone should have said no to the reclaim pausing feature for example, a broken feature implemented with an engine patch. Someone had to say no to snipemode.
Your development of a low stakes feature like a painting tool will of course be much smoother than introducing a whole new unit. If you think these things should work the same, we would already have many new units. We may even have Nomads implemented. Also just a note, the game is designed already. There is no role of game designer available. I was in charge of balance for a few years, I'm not a game designer and that wasn't the role.
I do think the balance team is somewhat dysfunctional, I think there are way too many talkers(who don't know enough) and not enough doers. I think there can be a no first approach rather than considering things and trying something. It's definitely frustrating to deal with as the game guy but I think it has to exist to provide oversight on what gets into the game.
I think there's a fundamental issue around what FAF is as a project. On one hand it is an open source development project that people want to work on and learn on but it's also a multiplayer lobby where substantial numbers of people have been playing for 10+ years. It's a unique situation.