You would need to identify the changes that you made so that after upgrading you can re-apply them if they are still necessary. I have several minor changes that I have made after upgrading for quite a few versions now.
Some times things change though, so your changes might not work. you would need to have someone that is versed in coding to fix them if they do not work.
As far as if the 3rd party SuperList plugin goes, you would need to reach out to the author of the plugin for support and compatibility.
