Changing some of the language within the revision viewer admin page revision.php

I resolved this in the end with some careful jQuery code that is run via a new JS file that is only loaded via the admin system pages.

To give an example of the jQuery code…

jQuery('.wrap a').each(function() {
    if ( getCurentFileName()=="revision.php" ){
        var text = jQuery(this).text();
        jQuery(this).text(text.replace('← Return to post editor', '← the new replacement text'));
    }
});

function getCurentFileName(){
   var pagePathName= window.location.pathname;
   return pagePathName.substring(pagePathName.lastIndexOf("https://wordpress.stackexchange.com/") + 1);
}