This one has eluded me for ages. I'm a barely competent MS-Word user, I want to update a series of articles I wrote in the past by inserting updates, thoughts, and comments in a single, different font, to clearly indicate the changes. Is there some simple way to do this?

Yes, this could be done with styles. Simply create a new style in a format that you like. Hopefully, you are familiar with styles but, if not, here are some references:

Understanding Styles in Microsoft Word
Tips for Understanding Styles in Word | ShaunaKelly.com

Hope this helps...

An entirely different approach, but one that also enables you to identify when an update was made, is to use 'Track Changes'.

__________________
Cheers,
Paul Edstein
[Fmr MS MVP - Word]

If using Styles to mark your changes, you would use a character style, not a paragraph style.