1- war state
If war exists AI becomes more angry, and sends more ships to attack you.
2- I've cause some battles by moving a ship on an ennemy ship.
If no treaty, ships must not cross or they will fight.
3- I'm not an english native speaker
Cool means "polite on the face, but angry inside" You are too close to their space, you have much more ships and planets, or they just don't like other people
4- What is the best way to declare a non aggression pact ?
Give small gifts first, as they become more happy they will accept treaty. Some races are just always angry
5- What's the use of warheads designed to be used by ramming into another ship ? I tryied it on my fregate, and i bumped into an escort : result : two ships destroyed ! I thought that kamikase area was over 'til 1945...
Should have worked, but maybe frigate is too small. Some armor will help it work better.
6- Do two research centers an the same planet provide two times more research points ?
Yes, more facilities(miner, farm, refiner, research), better result
7- Last but not least. Is it possible to refit an existing ship ?
Yes, design better ship of same hull size. Click green recycle button on button bar, retrofit is available
(updating missiles, cannons, engines and so on...). Is it possible to change the design of a ship without creating a new design name (which would not obliged me to have an escort I, escort II, escort III design vessels in the design list)
No, game needs new name to know which is which.