主要基于alireza ahmadi解决方案，但允许您同时更改多个产品：

var findCopy = 'Product Name';
        // The below is what I'm trying to achieve to get
        // var findCopy = 'Product Name (1+1)';
var targetThis = [...document.querySelectorAll('.copy')].filter(tag => tag.textContent.includes(findCopy))

targetThis.forEach(el => el.innerText = el.textContent + '  - 10% Discount');

<ol>
<li class="copy">Product Name (1+1)</li>
<li class="copy">Product (1+1)</li>
<li class="copy">Product Name</li>
<li class="copy">(1+1) Product Name</li>
<li class="copy">Potato</li>
</ol>

你知道产品名称吗 Product Name (1+1) ，因此需要找到具有相同值的标记，然后将其追加 - 10% Discount ```
var findCopy = 'Product Name (1+1)';
// The below is what I'm trying to achieve to get
// var findCopy = 'Product Name (1+1)';
var targetThis = [...document.querySelectorAll('.copy')].filter(tag => tag.textContent.includes(findCopy))[0]

targetThis.innerText = targetThis.textContent + ' - 10% Discount';

    var array = document.querySelectorAll('.copy');
    var targetThis;
    for (var i = 0; i < array.length; i++) {
        if (array[i].textContent.includes(findCopy))
            targetThis = array[i];
    }

    targetThis.innerText = targetThis.textContent + '  - 10% Discount';

我不知道您是否可以使用jquery。在这里，我使用jquery实现了一个解决方案。当然，它适用于多种情况
并改变它们
html:

<div class="new">
        <p>
            product Name 1
        </p>
        <p>
            product Name 2
        </p>
        <p>
            product Name 3
        </p>
        <p>
            product Name 1 abcde
        </p>
    </div>
<button onclick="test('product Name 1')">test</button>

js代码：

function test(string) {         
                $("p:contains('" + string + "')").each(function () {
                    var sHtml = $(this).html();
                    $(this).html(sHtml + " - 10% Discount");
                })
        }

最后，它将更改如下内容：
产品名称1-10%折扣
产品名称2
产品名称3
产品名称1 de-10%折扣