See attached 5.4.9 example QEX.

Below is some JavaScript code you can insert into a label on the same screen as your open-ended variable(s).

Using this script, it will insert a button with the label text of "Clear", right under your <input type="text"> or <textarea> fields (depending which one you're using on that screen).

<script>
document.addEventListener("DOMContentLoaded", function(event) {
 var inputs = document.querySelectorAll('input[type=text]');
 var textareas = document.querySelectorAll('textarea');

// Add a button for each input text
 for (var i = 0; i < inputs.length; i++) {
 var btn = document.createElement("DIV");
 var text = document.createTextNode("Clear");
 btn.appendChild(text);
 btn.className = "clearbutton";
 btn.onclick = function () {
this.previousElementSibling.value = '';
 };
 inputs[i].parentNode.insertBefore(btn, inputs[i].nextSibling);
 }

// Add a button for each textarea
 for (var j = 0; j < textareas.length; j++) {
 var btn = document.createElement("DIV");
 var text = document.createTextNode("Clear");
 btn.appendChild(text);
 btn.className = "clearbutton";
 btn.onclick = function () {
this.previousElementSibling.value = '';
 };
 textareas[j].parentNode.insertBefore(btn, textareas[j].nextSibling);
 }

});
</script>

This button is also styled by adding custom CSS into the "Options > Internet Options > CSS" tab:

.clearbutton {
 background-color: #4CAF50;
 border: none;
 color: white;
 padding: 15px 32px;
 text-align: center;
 text-decoration: none;
 display: inline-block;
 font-size: 16px;
 margin: 4px 2px;
 cursor: pointer;
}

Whatever text you want to use in the button can be changed in the JavaScript code. Also, how the button is styled can be changed with the CSS.

In my example, it should look and act like the below GIF:

Note: if you have multiple open-ended variables merged onto the same screen, each input box will have its own "Clear" button generated below it.