Made changes to a commit, performed commit amend. Do a push and I get the error:
! [remote rejected] master -> refs/for/master (no changes made)
>
It sounds like you are doing everything correctly as far as verifying you have made a change that Gerrit should pick up.
git push origin master:refs/for/master
Maybe this is the problem? If your changes aren't on your local version of the master branch, you aren't pushing your changes. Instead try:
git push origin HEAD:refs/for/master
HEAD is a shortcut that represents your current commit in git.