your intention is the opposite one

Thanks for not dismissing me as an idiot.
I played around with not overwriting styles until I managed to crash Scribus--first time that's happened!
Thing is, this is quite a long document. I've broken it into many smaller files. 20 chapters = 20 files. So the less modifying I have to do after import is important. Worse, I'll have to do another version of this book--same styles, different text--2 years from now. I'll never remember everything.
So what I want are distinct names for the styles. I've done this in LibreOffice, because their default style names are meaningless.
It seems to me the easiest way to go is to create 2 paragraph styles in LibreOffice, one justified, one ragged right, then change styles before I import into Scribus, 20 times. If you have a better suggestion, I'd be most grateful to hear it.