i have read that the overall of protein charge should be neutralized.
And proteins have more Ala, and less His, Cys, Pro, Ser and Leu than would be expected from codon multiplicities alone.
can i say that natural selection can change the code?
The proteins can hardly be neutral (if that’s what you meant), because
1) the charge depends on pH and different organelles have different pH
2) different proteins have different pI, thus they are not neutral