Here's my 2c with some ideas to procrastinate on.
When referring to COG, it really has no relevance unless comparing two identical track/wheel base vehicles or you own vehicle in a before after lift scenario. If you increase the height of COG above ground of your vehicle, you will reduce stability, which increase the ease of which it will tip over. Now increase the wheel track and you have decreases the effect of the COG raise on a side to side basis, but not on an end over end basis.
To work it out you are looking at triangular calculations. First you need to know what your current COG is - something that most will never know anyway, so sort of makes any calculations almost impossible anyway, so we progress on theory alone with no real numbers! (racing teams often need this information and it can be calculated by placing scales under all 4 wheels, raise the scales on side to tip the vehicle and now look at the shift in weight on the scales. This change in weight along with the angle can be used to calculate current COG).
If you picture your vehicle from the side or behind, and draw a line from the COG point to the road where the wheels touch and measure the angle of these lines at the COG point. If this angle decreases (ie by lifting the vehicle/ raising COG or by reducing wheel track / wheel base) then this will reduce stability. Not a difficult concept. It should be noted that like the laws on lifting a vehicle, there are also laws on reducing wheel track - in fact you are not allowed to reduce the wheel track at all without Engineering approval due to the reduction in vehicle stability - not that many people would do this anyway.
What is required to negate a lift (increase of COG) affecting the stability? Looking back at the imaginary triangle from before we need to keep the angle at the top the same, so lifting this point will require spreading the wheels out both to the sides and the ends (wheel base increase and wheel track increase). The ratio of lift to required track increase to keep stability the same changes depending on what the COG starting point compared to wheel track was. This is why I mentioned before without knowing what your COG is to start with makes the calculations impossible. Its not as simple as lifting 2in requires 2in wheel track increase to keep stability the same (although this is actually true if your COG height above ground happens to start at exactly half your wheel track!)
However, what is not as easy to work out is what effect any of this has in the real world on stability of your particular vehicle. A lot will depend on how close you as an individual push your vehicle to the limits of its stability. If you never get within 20° of the tipover angle of your vehicle, then lifting the COG will mean you no longer get within say 15° of the tip over angle, so no real change in capabilities of your vehicle in your hands. If you are an extreme offroader or drive really hard round roundabouts/corner and consistently run your vehicle right at its limits of tipping over, lifting the COG will most likely find you rolling onto your side or roof if you continue to drive the same way.
Now of course that is presuming that the lift you just put in has identical spring rates, because if you have stronger springs then you won't lean as much on an off camber run or when hammering it around a corner, so you would be less likely to tip than if you were running softer springs. Another reason for one of the lift regulations - the one that states the any replacement springs must be as stiff or stiffer than the stock ones.
So in all there is a lot to go into calculations, much more complicated than possible for most, and this is one of the main reason for legal lift limits without engineering, as the engineer will look at this increase in onroad rollover potential as part of the approval. Off road effects are generally of no interest to the Engineer.
So, clear as mud