I have a similar problem with the plugin. I am using a child theme of the twentyseventeen parent. As soon as I enabled the plugin for the child, the copyright completely disappeared from the theme! Much less me trying to edit the text. I even included this in my review of the plugin in the reviews section.
If you take a look at the php file that used to contain the copyright text and link in the first release of the twentyseventeen theme, you will see that in the latest version of this theme, it is no longer there! It used to be in ” wp-content / themes / twentyseventeen-child / template-parts / footer / site-info.php” The new site-info.php file is a carbon copy of the footer-widgets.php. The copyright has been hidden somewhere else now and the theme re-written to prevent it from being so easily modified. I am afraid that there are likely several other parts of the parent theme that have also been re-writen and the usefulness of this plugin for modifying the theme may now be suspect.
And, No, I cannot provide you a link to my implementation because I have created everything on a local debian server box just so I could get my site development done without endangering my live site. You could also take any unused old PC and turn it into a wordpress server for trying these things out like I did.
Looking forward to your fix for helping this plugin catch up to the re-writes of it’s intended theme target. I still think this is awesome work. It just needs a revisit.