[Andrés]

Copied from abilities.txt
Planet - Change Population Happiness
Value1 = Percentage the happiness of this planet's population is improved each turn.
Value2 =

Change Population Happiness - System
Value1 = Percentage change in population happiness for entire system (+/- percentage) each turn.
Value2 =

Didn't check if it actually works this way but this suggests you can give a happiness penalty to the entire system but not to a single planet.

I was planning to give most of the Imperial happiness penalties by making them use a special happiness type.
But this could be a good choice to balance their best shipyards: build faster or stick with the regular ones to avoid making the population even angrier.