PHP - disable_functions

I'm trying to disable functions, exec, system, passthru, etc. I have seen, on-website topics, to do it in a PHP.ini file. I don't have this file but I do have an init.PHP. I'm on a shared site, cPanel GoDaddy. Can I put a file, don't know the file name should be, in my public.html directory. This is where my Form Community, Invision Community, is located? And how would the code look? Never have I done this before. I'm Totaly Green. Bob