title: Security against backward-changes in git?
body: <p>In particular, is it theoretically possible to make changes to the central (bare; or not) git repository (i.e. having full access to the system it is on) so that the changes do not appear (as a commit) / do not cause conflict on update, but appear in newly cloned repositories?</p>
  
  <p>Or any other similar “forgery”-like change.</p>