Iron deficiencies typically exist if the soil is not acidic enough, not when it is very acidic. A high pH binds the iron, making it unavailable for uptake, so pH is lowered to offset that.

You can use a chelated iron product to offset the chlorosis, although I am not at all convinced that the yellowing is due to a lack of iron.

Just leave the soil mix alone. My 30 plus years of experience are telling me that you are far too intent on messing with soil conditions unnecessarily. Camellias do not require a highly acidic soil at all. They grow perfectly well here - with zero chlorosis - in only mildly acidic soils. Right around 6.3 to 6.5 is fine.

Don't turn every gardening experience into a science or engineering experiment. As long as you provide decent drainage, a moderately fertile soil, enough water and appropriate light conditions, you should be able to grow just about anything suitable to your locale without so many issues.