I have backup and restore Bitnami Moodle before upgrading the Moodle version.
If I need to upgrade the Moodle version, would I need to redo the edit in index.php?
Sorry for the late reply. I had a long weekend 
Yes it is true that you would need to maintain customizations when upgrading Moodle. This is part of the bigger picture to consider when deciding whether to introduce customizations.
Thanks for clarifying Jamie!
This means I have to record all core codes changes.