With the overridden text still selected (you'll see a + next to the Character Style name in the Character Styles panel), choose Redefine Style from the Character Styles panel menu.
Why are you using Character Styles for headlines? Why are you not just applying the correct Paragraph Style without any Character Style?
If, for example, you have one paragraph style applied to all titles, and after make local changes you decide that you really like this new formating, you can redefine the style:
select your text formated with the style you want to redefine > in the Styles panel menu choose Redefine Style
If I didn't understand good your question, can we see one your title before and after?
Oh man, can't believe I missed such a simple feature, d'oh.
Thank you so much for taking the time to answer!
Imagine you have to change the font of, e.g., 103 para styles, iyo, what is your best way to do this?
… I forgot: 89 char styles too!
… and so … redefine all these styles!