There should be an occupation phase (to last24 ticks after a planet is taken) where the population is in a state of rebellion; where every tick there is a battle and where the stationed ground forces fight the pop. Something between a ratio of 1%to5% of ground forces to the population would be necessary for the occupying forces to win these battles. Just as in any battle, a certain number of population and stationed forces would die every tick according to the respective size of forces. Depending on population growth bonus, it could become more difficult to overthrown their occupiers each tick if the amount of pop they lose in their battles each tick is greater than the amount of new population that grows each tick. With a high pop growth bonus, say anything over 0% the pop still grows in spite of their losses each tick if say they fight 5% of ground. Therefore, even though 5% of ground is stationed the first tick, if the population growth is high and outpaces losses, the ground forces might only be 4% the following tick, and, therefore, the population's rebellion would be successful. Thus sometimes, the player would have to calculate how many forces they would need to station to hold the population according to the target empires population growth bonus (not the occupier's pop growth bonus). However, if number of ground forces stationed is higher than the minimum required (like 100% the population instead of 5%), the entire population might get killed off in one tick. In this case, the occupation phase would end that tick and the planet's pop would reset to 0. I would laso think the buildings should get destroyed. Both the planet and the population would be considered naturalized. In this way, a would be occupier has the option of trying to hold the population and the infra and profit by doing so, or just killing them off and starting from 0 pop and 0 infra. It might prove to be better for the occupier because they would have to station 100% ground forces:pop for only 1 tick to kill them off and rest the planet to 0, and so their ground forces can be used elsewhere the next tick.
Now, if the player doesn't station much more than the 1%-5% required to to fend off the population, battles would continue to occur every tick for 24 ticks after a planet has been taken until such time as either the pop dies off due dying more each battle than what is produced according to their population growth bonus, or until the population wins an occupation battle. After 24 ticks, the period of time it would take for the population to become amalgamated into the occupier's civilization, the occupation phase would end and the planet and its pop would be considered naturalized.
If at any time over the first 24 ticks the pop won any of the battles, a number of things might happen:
1. a chance that the pop would escape and blow the planet
2. a chance the pop would escape but fail to blow the planet and leave the planet with infra intact to the occupier
3. a chance the pop would escape but fail to blow the planet but succeed in lowing the infra
4. a chance the pop would overthrow their occupiers and take control of the planet the planet, with infra intact, would revert to the empire that had lost it
You could do other cool things with this:
You could have an op called "sponsor rebellion" or "incite insurrection". This could be used by say only the Quantam (each race should have a special, race specific op, I think). The op could be used only during the first 24 ticks after a planet has been taken. It would be considered an offensive op and would break a fam's overseer protection if successful or if discovered. It would not have to be issued by the empire nor the fam that lost the planet, but any Quantam of any fam of any empire. Like the spread false info op, the Quantam opper wouldn't have to take the planet him or herself, but could choose which empire would receive control of the planet, as long as that empire would be a member of the oppers family (this could be used for intra-fam planet swapping btw).