Sallen-Key LPF Q factor and gain
dumping factor = 2/Q. Assuming that these are correct.


It's called damping factor not duping or dumping and no, what you have written is not correct: -

$$\zeta \text{ or "damping factor"} = \dfrac{1}{2Q}$$


Yes
The damping factor is commonly changed by altering the ratio of the two capacitors (for instance). Or you can change the resistor ratio


Because the two values are multiplied together to contribute to the un-damped natural frequency, increasing one while decreasing the other will change damping (or Q) without altering the frequency.