Adding cool boiled water to boiling water

I’d say no on the basis that the reason you use boiling water is to kill bacteria in the formula not the water and the manufacturers suggest how much water you need per scoop. On a practical side too, let’s say you are making a 180ml bottle which is 180ml water, 6 formula scoops. If you are using cooled boiled water are you using less actual boiled water? Then how do you measure you are putting the exact shortfall of water in (using another bottle)? Because if you didn’t then it’d be too thick or too runny and then it’s constipated or diahorrea ridden baby.

It’s trial and error to find what works best for you. I was told not to use boiling water as it can damage the formula (maybe the protein?) so to use just off boiling. For time purposes I devised a water ratio and although I can’t remember exact quantities it was something like 4oz boiling, 1 oz cool boiled, add powder (8 oz worth) and shake, top up with 3 oz cool boiled.
It made a ready to drink bottle in 2 minutes.

And yes, I had 2 bottles one to do the mixing in and another with the amount of cool water needed to add

It's adding boiling water to formula and shaking, then topping up with cooled boiled water for the rest. Ratio of 1:3. Essentially copying the perfect prep machine.

I used to do this when out and about to mimic the perfect prep. I mixed the formula in 2 or 3oz of boiled water (used a flask) and then added the cool boiled water from another bottle.