If it's public, there's no telling rather the GM add it to their blacklist to ban you.
But yes, usually crosshair modding are (usually) bannable. If you don't want to take a ban risk, code your very own crosshair hack so they cannot detect it. Cross hair hacking is easily done anyway, why get a public one?
Best advice I could give is testing it on a mule account, and if you feel that you can say the test is done and that it's not bannable, then you're free to use it on a main.