Nofollow’ed External Manually: Would the plugin create duplicate nofollow tags?

Hello,

I recently decided use this plugin, but something clicked my mind before I attempt.

The thing is, I have always manually nofollow’ed external links in the past (this is by manually adding the nofollow attribute in the “Text” tab of WordPress editor).

Now, if I do install this plugin and nofollow all external links using it, would it inject another “nofollow” tag in the previously nofollow’ed links? Or will it ignore them as it may detect the nofollow parameter is already present?

Thank you