Just so you know, the code that I wrote(which I did right then), doesn't do anything in 1.13e(the offsets are wrong). However, if someone did find a way to inject it into 1.13f, it would be a button action that changes the ID(not graphics) of the unit to the act var that is passed(just so you know what it does). (With one minor change....It should be 0x6a48a0, not a8 at the end...)
If you're serious about learning this aspect of modding, I suggest you learn assembly in and out. Because that's about the only way you'll find the offsets(unless I give them to you...but I'm not going to do that...you won't learn anything that way...this isn't to be mean, I just don't readily give out offsets to just anyone). Then, just start messing around in a dissassembly of the exe, looking for stuff. However, what you've seen/learned is not enough to do what you want. What you'd need to find is a way to edit the existing code(kinda like SCR did), and remove the distance restriction. Well, I know that the distance is going to be in FG, but I haven't found it yet, so that's as far as I can go.
As for your 'idea' on how this works, that' won't fly. It would only work in single player. The best way to do this would be to completely copy the build orders, change what you need, then make the unit use those orders via a custom netord(there's only 1 unused one...), and then it would work multiplayer. Now, I don't know how much of those term you understand right now, but it means about the hardest thing in modding, multiple custom injections of code into rigid code structures. Not fun. I've never done that...but eventually FG will be able to do that without all the hassle(note, this is only planned, it's not the most important thing).