At the moment its not possible to change the tax rate of planets, Salaena1000 asked on irc about being able to change the tax rate on planets, personally I think changing the tax income of planets would be a very good idea, and is coupled with culture, higher the culture the more you can tax a planet, but low culture and low alliance to your empire and you tax them hard, will make the planet revolt, I think this will add more to the gameplay, so what do others think?