To back up what SamBC said:
Civ5 XML modding is done differently than earlier games. You do NOT modify the core game's files, and you don't duplicate the old file and make changes. It's a simple Update system. For more detail, go read Kael's modding guide, stickied over in the Reference forum. It's a little out-of-date in a couple areas, but it should explain the concept of XML modding pretty well.
Given that, it's rare to see a mod get truly large; unless you're going for a total conversion type of thing, the vast majority of the XML database will remain unchanged from the vanilla game. This also means that the number of files containing values to be changed is irrelevant; if you want, you could stick every change in a single file and name it Bob.xml, and the mod would still work as long as you set it up correctly.
Now, in larger mods (like mine) it's generally just more convenient to mimic the existing tree's structure, but you don't HAVE to.
I am going to download your mod because it looks awesome, but i have one question about it. Can i choose the era when the game ends? and if its no possible, are you going to include this option in the future?
No, and no. I'm not trying to be dismissive here, but my mod's entire concept is built around progression towards the Transcendence victory at the end of the tech tree. In fact, I've tweaked the Advanced Setup menu so that that victory condition is always on and it doesn't even give you the option to disable it. (Not that you can't win plenty of other ways; I've NEVER actually reached Transcendence naturally, only when I deliberately chose not to win some other way.)
Given that, it really wouldn't make sense to let anyone stop the tree partway through. However, I did drastically change how research progresses, so you'll spend a bit more time in each era than you would in the vanilla game, and units don't obsolete quite so fast because of how I've laid out the tech tree.
Now, to be clear, my mod is actually two separate mods: a Content mod containing all of the future-era content (and the really complex Lua code), and a Balance mod that does things like the research slowdown I mentioned. The Balance mod includes many changes designed to make the game less winnable in earlier eras; for instance, in my mod all units get a "Home Field Advantage" promotion that gives them +10% when defending in friendly territory, increasing to +20% when ATTACKING in friendly territory (i.e., counterattacking against invaders). Also, instead of adding +2 to a city's Defense, the Palace now adds +10. With those two simple changes, early-game conquests become FAR more difficult, and it becomes very rare that any civ reaches an insurmountable power level before the Industrial (and still pretty rare at that point).
My point was that if you wanted to have a game stop at the Renaissance, then you'd want to reverse that sort of thing so that a military victory by the Renaissance is possible; give all units +10% when attacking, for instance, to encourage military offenses.
