No.

one requirement is hardcoded, I already asked for the option to use more required techs for more complex tech trees, no answer yet and the thread is somewhere on page x already, not even one answer, not even from someone who like the idea

more than one ability bonus should be possible, since there are techs like "Star Federation" that give both influence and diplomacy bonuses.

yes you can rewrite techtree.xml. if you want to add a bonus you don't see an example of, use the ability names in raceconfig.xml

what bugs me is that the ability bonuses in the political party file are all numbered. i think the parties could be rebalanced a bit personally.

Unless they changed it to ignore multiple requirements in v1.2, you can have more than one. I tested upto 4 requirements on a single tech. All you need for it to work is additional requirement tags, nothing special. The problem is that the tech tree display gets a little messed up and I have a screenshot showing it @ http://www.gc2builder.com/vtopic-90.html A large tech tree with many techs that have multiple requirements will get messy fast, but it works perfectly you would expect. Crossing categories with your multiple requirements makes the tech tree display even more messier and confusing.
I've tested and confirmed this with v1.0x, 1.2 beta 1, and 1.2 beta 2 (I highly doubt they took it out of 1.1 only to put it back in 1.2). Planetary Improvements, however, do not allow for multiple requirements.

Can the branches converge?

In the previous example I gave there were two branches to the beam weapons tree. The tree branching off into either more plasma or phasors in that example. Can the two lines converge at some later point back into one, at the doom ray for example?

It says you're supposed to get a +75% bonus for mil.,soc., and res. in a Star Federation. The only thing I think that you get is a +75% bonus to economy since production doesn't increase, just the amount of tax revenue I receive

This is "working as intended" as far as i know. From what i've read, goverments were changed but they didn't update the text. I haven't checked if they fixed the display or not.

@syneris: Thanks for the clarification. That makes perfect sense now that I think about it. I guess for the two-pronged beam tree, one would have to create two doom rays, one for each branch ending. Unless a different weapon was modded to fill one of the slots, in order to make two unique lines. Perhaps I could tap the elusive subspace annihilator for that role.

*sounds of gears turning*

Thanks for all the input. I really wish it was possible, it would open up much more modding possibility. I was thinking to write in some techs to make the tree more interesting, personally I don't like simple branched trees and generic names like "Warp Drive IV." But now, I am lost!

Thanks again, and Frogboy, consider changing this?

@syneris: Ok so that makes the dual doomray option a no-go in my opinion, however, I do see a way a branched tech tree could be accomplished with relative ease. Each branch has to diverge and then go it's seperate way and end with its own unique tech. In my running example the subspace blaster and annihilator could be moved to one branch of the tree and modded to be the top tech while the doom ray's research costs could be modified to offset the change in the other branch. Let's say that at plasma III, one can decide to go with phasors or continue down the plasma route. The two weapon types can be differentiated by making plasma weigh more, do more damage, and cost more than same level phasors, or vice versa. For example, use "Plasma V" that is a size 7, sizemod 4, damage 4, and costs 70; or Phasors III which is size 5, sizemod 4, damage 3, cost 40. Depends on which path you go down. One ends in a doom ray, the other ends in a comparably modded subspace annihilator.

That's my idea, anyway. I'm going to try it right after I finish the current galaxy I'm playing.

Sounds like a good idea to me.