Hi leaf.
This might not start off answering your question but please keep reading.
I think it's better to use styles with regards to their meaning within the document rather than what they do with the text.
For example, if you have a character style that makes text bold and you call it "Bold", then apply that style to the text it makes sense at first but if you then want to change all of the bold text to, say, italics, then your "Bold" style name doesn't make sense any more and will cause confusion.
It would be better to think about what the style is for and then name it accordingly, e.g. "Image Caption", "Emphasised", "Phone Number", "Sidebar", etc. That way, if you need to change the formatting of a particular style, you can do it easily and the style name still works.
Of course, this doesn't help if you've manually set some text to, for instance, bold, in the Properties and you want to later change it - as I believe is your intention - but your problem really demonstrates that styles should be some of the very earliest things you should set-up in your document.
They only take a few seconds to set-up and can save so much time in the long-run. You don't even have to set them up correctly at first. As long as you start using them from the beginning you can change them at any time as necessary.
I realise that this doesn't solve your current dilemma, and you could well be an expert in styles. My advice is more for the people reading this who find themselves having to do the same thing as you are asking about.
With regards to your feature request, unless it's already being thought about (and it might well be), I'd suspect that it would be a low-priority item. However, it could be a good student project as I'm sure it won't be as simple as it first sounds.
Anyway, apologies if I've been preaching to the converted but I really think that good style management is something that should be given higher visibility in the Scribus documentation. Styles are so powerful that not using them is a real shame.
Garry.