Retain revision author when editing revision
You definitely don't need to copy, replace, override, etc.

Node revision information is handled here.  As you can see, the revision author is maintained, but most use-cases will call to show the original author.

Depending on your situation, there's many ways to show the revision author instead.  For example, I see that the revisioning module you're using provides a revision-author token in revisioning_tokens.inc.

Other possibilities: hook_node_view in a module, template_preprocess_node in a theme's template.php, node--NODE-TYPE.tpl.php, etc.

Edit: BTW, if you went about updating the author ID like you mentioned, you would effectively change the ownership of the node to another user, which probably isn't a good idea!