Q:

How to make sure others people cannot edit my git notes?

I want to do the release notes by using git notes, but I am not sure if other people change my git notes by using the same ref. 
BTW, chmod 444 .git/refs/notes/abc_test & .git/logs/refs/notes/abc_test does not work.

A:

I don't think you really can protect published git notes.
What you can do is put them in an explicit namespace, as mentioned in here:

I think for "typical usage" one stores others' notes in a different place anyways, e.g. I store Thomas' list-notes in refs/remotes/trast/notes/ so that they don't interfer with my own notes.

If in the same namespace, then they can be merged:
git checkout refs/notes/commits
git fetch origin refs/notes/commits
git merge FETCH_HEAD
git update-ref refs/notes/commits HEAD
git checkout master

But that would change their content.

