如何更改数据工具提示消息

当然可以。使用（content: attr(data-tooltip)）从属性data-tooltip获取的属性文本。

因此，您只需要将属性的值更改为您想要的值。

function changeTooltip() {
  document.getElementById('abc').setAttribute('data-tooltip', 'aaa');
}

/* Add this attribute to the element that needs a tooltip */
[data-tooltip] {
  position: relative;
  z-index: 2;
  cursor: pointer;
}
/* Hide the tooltip content by default */
[data-tooltip]:before,
[data-tooltip]:after {
  visibility: hidden;
  -ms-filter: "progid:DXImageTransform.Microsoft.Alpha(Opacity=0)";
  filter: progid: DXImageTransform.Microsoft.Alpha(Opacity=0);
  opacity: 0;
  pointer-events: none;
}
/* Position tooltip above the element */
[data-tooltip]:before {
  position: absolute;
  bottom: 150%;
  left: 50%;
  margin-bottom: 5px;
  margin-left: -80px;
  padding: 7px;
  width: 160px;
  border-radius: 2px;
  border: 1px outset #C0C0C0;
  box-shadow: 3px 2px 5px #9F9F9F;
  background-color: #000;
  background-color: hsla(206, 73%, 34%, 0.9);
  color: #FFFFFF;
  content: attr(data-tooltip);
  text-align: center;
  font-size: 11px;
  font-family: "Trebuchet MS", Helvetica, sans-serif;
  font-weight: bold;
  line-height: 1.2;
}
/* Triangle hack to make tooltip look like a speech bubble */
[data-tooltip]:after {
  position: absolute;
  bottom: 150%;
  left: 50%;
  margin-left: -5px;
  width: 0;
  border-top: 5px solid #000;
  border-top: 5px solid hsla(206, 73%, 34%, 0.9);
  border-right: 5px solid transparent;
  border-left: 5px solid transparent;
  content: " ";
  font-size: 0;
  line-height: 0;
}
/* Show tooltip content on hover */
[data-tooltip]:hover:before,
[data-tooltip]:hover:after {
  visibility: visible;
  -ms-filter: "progid:DXImageTransform.Microsoft.Alpha(Opacity=100)";
  filter: progid: DXImageTransform.Microsoft.Alpha(Opacity=100);
  opacity: 1;
}

<a href="#" id="abc" data-tooltip="abc"><img src="http://www.w3schools.com/images/w3schools_green.jpg"/  ></a>
<br />
<button onclick="changeTooltip()">Change tooltip to "aaa"</button>

如中所述https://developer.mozilla.org/en-US/docs/Web/Guide/HTML/Using_data_attributes数据属性可以通过dataset对象访问，使用属性名称在data-之后的部分。

在您的示例中：

var tlink = document.getElementById('abc');
 
tlink.dataset.tooltip = "def";

/* Add this attribute to the element that needs a tooltip */
[data-tooltip] {
  position: relative;
  z-index: 2;
  cursor: pointer;
}
/* Hide the tooltip content by default */
[data-tooltip]:before,
[data-tooltip]:after {
  visibility: hidden;
  -ms-filter: "progid:DXImageTransform.Microsoft.Alpha(Opacity=0)";
  filter: progid: DXImageTransform.Microsoft.Alpha(Opacity=0);
  opacity: 0;
  pointer-events: none;
}
/* Position tooltip above the element */
[data-tooltip]:before {
  position: absolute;
  bottom: 150%;
  left: 50%;
  margin-bottom: 5px;
  margin-left: -80px;
  padding: 7px;
  width: 160px;
  border-radius: 2px;
  border: 1px outset #C0C0C0;
  box-shadow: 3px 2px 5px #9F9F9F;
  background-color: #000;
  background-color: hsla(206, 73%, 34%, 0.9);
  color: #FFFFFF;
  content: attr(data-tooltip);
  text-align: center;
  font-size: 11px;
  font-family: "Trebuchet MS", Helvetica, sans-serif;
  font-weight: bold;
  line-height: 1.2;
}
/* Triangle hack to make tooltip look like a speech bubble */
[data-tooltip]:after {
  position: absolute;
  bottom: 150%;
  left: 50%;
  margin-left: -5px;
  width: 0;
  border-top: 5px solid #000;
  border-top: 5px solid hsla(206, 73%, 34%, 0.9);
  border-right: 5px solid transparent;
  border-left: 5px solid transparent;
  content: " ";
  font-size: 0;
  line-height: 0;
}
/* Show tooltip content on hover */
[data-tooltip]:hover:before,
[data-tooltip]:hover:after {
  visibility: visible;
  -ms-filter: "progid:DXImageTransform.Microsoft.Alpha(Opacity=100)";
  filter: progid: DXImageTransform.Microsoft.Alpha(Opacity=100);
  opacity: 1;
}

<a href="#" id="abc" data-tooltip="abc"><img src="http://www.w3schools.com/images/w3schools_green.jpg"/  ></a>

var anchor = document.getElementById('abc');
anchor.onmouseover = function(){
   this.setAttribute('data-tooltip', 'hello sir');
};

小提琴https://jsfiddle.net/omarCreativeDev/6rpxLu4p/