Wanted to chime in here with a personal anecdote: A few months ago I took over managing a Discourse forum where I work. The forum is used seasonally, for about 5 months, then not touched for 7. When I took over we were having all sorts of intermittent issues. After the forum went “partially down” 3 times in 4 days, it was decided that I’d work with our IT staff to figure out what was wrong. Almost 6 hours later, we found that a former dev modified Discourse files, set them to overwrite the existing Discoures files each update, and this was the cause of our issues. 4 days of nearly full-time work later, we’d managed to stop the files from being overwritten, develop a plugin, and get everything working again.
Why am I sharing this? I just want to emphasize that modifying Discourse is unsupported (read: not a plugin) ways is bad. While we only had a few files modified, it caused us major issues that fortunately were caught before our forums went live again for the season. Please take the time to un-modify your install, put the changes into a plugin, and only then attempt an update.