Change table_definition_cache limits question

Hi Greetings to all is my first post and I am a Cpanel user for 4 months and I speak very badly English know apologize. Well I start asking, why can not change the limits of table_definition_cache and open_files_limit? simply from the my.cnf. I have read several messages in this forum that talk about the topic, I have tried everything explained here ... and nothing. Now I doubt if Cpanel was designed for dummy and should not change those varibles easily. I asked my service provider to make the changes, imagining that they have more expiration and almost destroy all the DB, so I'm not the only one not to understand what Cpanel's do. Well, I hope to find someone here that explains how to make these changes step by step please. Thanks