var target = document.querySelector('body');
var config = {
  childList: true,
  subtree: true
};

var observer = new MutationObserver(function(mutations, self) {
  mutations.forEach(function(mutation) {
    if (mutation.type === 'childList') {
      var elements = document.querySelectorAll('#js-pull-merging .primary.merge-branch-action');
      Array.prototype.forEach.call(elements, function(element) {
        if (document.getElementsByClassName("js-issue-title")[0].textContent > -1) {
          if (element.className.indexOf("primary") > -1) {
            element.className = element.className.replace(/primary/g, 'disabled').replace(/js-details-target/g, '');
          }
        }
      });
    }
  });
});

observer.observe(target, config);

@@ -307,16 +307,8 @@
 ing 
-.primary
 .mer
@@ -468,16 +468,31 @@
 tContent
+.indexOf(%22WIP%22)
  %3E -1) %7B
@@ -676,24 +676,214 @@
           %7D%0A
+        %7D else %7B%0A          if (element.className.indexOf(%22disabled%22) %3E -1) %7B%0A            element.className = element.className.replace(/disabled/g, 'primary js-details-target');%0A          %7D%0A
         %7D%0A  

support to trace changing PR's title