This would not be specific to Netbeans, but you can configure your local repo to prevent pushing:
git remote set-url --push origin no_push
As for the update, unless you setup some kind of webhook on the remote repo side (which a simple repo does not have, contrary to a Git repo hosting service like GitHub), you would need to fetch at regular interval.
If you don't need to be in sync at all time, you can simply pull and rebase before pushing.
git config pull.rebase true
git config rebase.autoStash true
Again, not specifc to NetBeans, but Netbeans will take into account those local Git repo settings.
If someone wanted to manage a Git repo with one Git server, such as Git for Windows, but read-only use the repo with Netbeans.
One simple answer: take an archive of your repo and unzip it somewhere for NetBeans to use: this is no longer a Git repo, and NetBeans does not risk to add any commit to it.