I have an HTML field called 'preview' that depends on another field and needs to call an API every time it changes. I want to change only certain elements within the 'preview' field. How can I achieve this?

for example

after changing some field, the preview field contain 

<p style="background-color: yellow;" id="warning-a">(Warning) Something happen and you should change this and that</p>

<ul>
<li>Some data</li>
<li>Some data</li>
<li>Some data</li>
</ul>

The warning should be removed after a certain action is triggered, which does not involve calling the API.

I aim to use as few APIs as possible.