Do you have the latest version? In test_char_4 there are 3 examples on how to do this :) Not all of these functions exist in older versions.
Noticed right after I sent the comment. I've been tinkering with it and found something that can work. Thank you for all the work you've been putting into this!
Also, somewhat unsure if I'm the one making a mess of the code you presented but I've noticed that after I did the contact name change, whenever I leave the chat, it shows this instead of the changed name "Junichi"
Its been changed to a group chat so its using the group chat name, this means there is either 1 member, or 3+. Make sure that when you remove a member you add another one, and if you add another one you remove the original one. If you shift+o for the console (this causes a rollback so make sure you click to advance dialogue once before you do) and type conversation_name['members'] (obv replace conversation_name with what its actually called) then it will print the members out for you, and you can check.