I can only answer for GUI interaction because I don’t practice command line.
It depends on how the DOCX is formatted.
If you use Word paragraph styles, just change the paragraph styles configuration. This will work if you have no other formatting, e.g. you changed font on a single word, because Word has no notion of character style. Every thing overloaded on text is done with direct formatting which can’t be controlled centrally.
On a computer where your “offending” fonts are not installed, you can create a replacement table with Tools
>Options
, LibreOffice
>Fonts
, but this does not change the document itself. It only provides a substitution for this session.