You are my hero, thanks very much, working!

• Find = <li class="h6">(.*)</li>
• Replace = <h6>$1</h6> – the $1 takes the contents from the first matched parentheses group, hence “shall not alter different included text”
• ☐ . matches newline disabled

It should work as desired – the included text stays the same, but each pair of <li...>...</li> changes.

With

• Find = <li class="h6">(.*)</li>
• Replace = <h6>$1</h6>
• ☑ . matches newline enabled

it will match the first <li ...> and the last </li>, which is not what you want

With

• Find = <li class="h6">(.*?)</li> – the ? limits the .* to the smallest possible match
• Replace = <h6>$1</h6>
• ☑ . matches newline enabled

it will match each <li ...> and its paired </li>, similar to the first example.

Either the first or the third should work for you.

This animation shows those three examples in practice, with the first and third working the way I think you want:

Please note that nested li will mess it up: for example, <li class="h6">blah <li class="embeded">yada<li> blah</li> will not replace correctly. Adding nesting to the regex will be nasty; if you need it, @guy038 should be able to help; otherwise, hopefully what I have will work for you.