By it's very nature, anything that is only client-sided will not appear to anyone else. If you made yourself invisible with a client mod, everyone except you could see you as if you hadn't done anything. Great if you want to make fancy screenshot poses, though useless for just about anything else.
If you want to be invisible to everybody, you have to get the server to make you invisible, which might be impossible if the host doesn't want you invisible. Fully transparent avatar colours might work, IF the server accepts them. Also, IF the admin(s) of the server accept them, once they find out that you have them.