For example I know that 'safe greenhouse gasses' warms up an atmosphere but will a certain amount of greenhouse gasses continue warming the atmosphere or does it warm the atmosphere to a certain level and then level out? Also is it possible to take gasses out of an atmosphere instead of just putting them in?
Changing the atmosphere by x will have f(x) effect, and that's it. It's not an ongoing process, unless you are continually adding (or removing) more gas - with the corollary that changing the hydrosphere (ice sheet to liquid, or vice versa) will have secondary effect on temperature (via planetary albedo) that may take a few construction cycles to work through (due to the recursive nature of the calculations).
So if you turn off terraforming the temperature will hold where it is. And yes, you can remove as well as add, that's why there's a checkbox titled 'Add Gas to Atmosphere' - leaving it unchecked removes the specified gas.
