Is it possible to patch a non-dev version of a module?
There would be a few differences from the process described on that documentation page.


In Step 1, when creating the topic branch, specify the commit from
which to create the branch. You can do this by appending a commit
ID, a tag name, or an existing branch name to your git branch
command. Tag name should work, because Drupal project releases are
tagged with the project version number. So if you wanted to patch
off of the 7.x-1.5 version of a module, instead of this:


  git branch [issue-number]-[short-description]


You would do this:


  git branch [issue-number]-[short-description] 7.x-1.5

You would skip Step 4 and 5, since those steps are for making apply
to the most recent dev version.
In Step 6, when using the git diff command to create your patch
file, you now want to diff against the commit that represents the
unmodified version. Again, we can use the tag/version name.


  git diff 7.x-1.5 > [project_name]-[short-description]-[issue-number]-[comment-number].patch