I'll give my 2 cents: you can do this with javascript, but it won't be easy. You will run into several issues that will make this challenging.

My thought is that you can modify the text using javascript based on some condition that you respond to (say, a change event on the drop-down you're using). The column header is easiest, but if you have "text under" the field, you will need to loop through all the rows to change everything.

Also, any time you add a new row, it will be added with the original "text under" so you would need logic to handle changing it properly for adding new rows.

Finally, you need to be aware that when you submit the form, the page gets reloaded before the image is generated. You will have to build some logic that ensures the text gets modified properly when the form gets reloaded. One way to do this is to add hidden fields to store data in as the form content gets dynamically changed, and then check this hidden field when the form loads to re-apply the changes. If you search a few posts on here, you can find information about each of these pieces, although I don't have time to put all the code together for you here today.