Yes and the second is in reference to Writer, because both are from the LibreOffice help documentation. Regex is old functionality that is generally built in by default into applications such as Word and other word processors for situations such as these. So unless Libre specifically states otherwise, there’s no reason to believe this basic default functionality doesn’t exist and it’s just a matter or where.
If you’re unsure how to implement and use the functionality, or that it exists in the first place, that’s fine. Because the regex functionality isn’t actually what I’m trying to accomplish, just something I thought may achieve a solution to my problem, which nothing you’re suggested has. It’s likely I’ll have to write a separate little script outside Libre to accomplish what in my mind should be basic functionality.
Here’s some further reading on Regular Expressions (Regex) should you feel inclined - https://en.wikipedia.org/wiki/Regular_expression