Yes, changes to that file will be lost on updating.
You could create a custom admin theme and insert it via JavaScript but, unfortunately, there is currently a bug with inserting custom JS -
bugs.limesurvey.org/view.php?id=13389
. When the bug is resolved, I'll provide a little script.
Cheers,
Tony Partner Solutions, code and workarounds presented in these forums are given without any warranty, implied or otherwise.
The following user(s) said Thank You: Deusdeorum, korsakov14