I'm sure one or more of the more experienced Scribus people will probably have a good solution for you but if I can add something from my own experience…
When I first started using Scribus I didn't use the Styles because I thought they were a bit too long-winded to set-up (for the simple stuff I was doing then anyway).
Then I started doing more complicated things and decided to take the jump into getting to know more about Styles and I'm really glad that I did. (Even if I'm in no way any kind of expert with them yet.)
Once I got over my initial reluctance to use them, because they looked too complicated for what I was doing at the time, I came to realise quite quickly how powerful they were.
For instance I could totally change the look of a whole document by simply making a small change in one place; a massive time saving when trying different "looks" out. (In your example you'd only have to change three styles once each to make the change you're after; one paragraph style and two character styles if I've understood you properly. A few button clicks and it's done; make Scribus do all of the repetitive hum-drum work for you.)
Also, I could control my use of fonts by knowing which fonts were used by which styles. Sometimes I'd use some similar fonts when "playing around" and forget that I'd used them, then later they'd be embedded in my PDFs, unnecessarily adding to the file sizes. For instance, I regularly use a font with "Regular" and "Medium" and "Book" weights that are very similar when viewed on the screen and each one added to the size of the PDF (10-100K each if I remember right). It doesn't sound like much but it can add up, for example, server-throughput-wise if you've got something that's downloaded many times.
Anyway, to cut a long story even longer!, I'd really advise using Styles as much as you can right from the start of a document. It will be a big time-saver in the long run and could save a lot of headaches. (Even if you never change the style from start to finish it's something you'd only need to set-up once.)
Even if this doesn't help your current situation I hope it will help someone browsing this forum for similar help in the future.
Garry.