I’m sure someone has figured this out, but it really is not recommended to edit assets in this way. There is a chance the format would change between versions but more importantly, the chance of human error is massive. You’ve already seen how a seemingly small change will break it (presumably because of the serialisation systems used).
If you really want to know how to change it, then a bit more information about exactly what you want to change would be helpful. Changing a string is one thing, but changing references to other assets is something else.
I’d suggest the best approach is to work out how to alter these within editor itself. If you’re looking at locating spelling errors or changing text, maybe look at the Localisation System in UE4. If you’re looking to make bulk changes, maybe the bulk editor is enough. If it’s something more custom, maybe a Bluetility to make those changes is the way forward (I’ve recently done some asset edits via Bluetiltiy myself and was pleased with the result).