What’s the exact message you’re seeing and at what point in the rebuild does it happen?
I just started up a VM I use for testing and modified the line, then rebuilt. At the point where launcher updates itself, it did the git pull and did a fast-forward merge as I expected, leaving the modification intact.
The version I was updating from didn’t include a change to launcher itself but I would expect that to work the same way as long as there isn’t a conflict, i.e. as long as that exit 1 line or very nearby lines aren’t changed in the repository.