Topic updates and personal changes

Hello! Tell me, we are in the topic made a lot of changes, but there are frequent updates and changes are reduced to the standard. And again have to sit a long time to sort through the files to make adjustments to make it look right. Is there a way to make all of our changes have remained even after updating the theme and do not have again to fix it!? Thank you!

I managed to find the plugin “Child Theme Configurator”, thanks to it I create a child theme and when updating everything remains the same as it was, only the problem is in the function.php file and the settings, they are not saved. And copying and pasting the code, errors appear and the site does not open. Can you tell how to add his codes to a child theme? Thanks!