@hfpop - why would you not just use the series name column for both those examples?
e.g.
title: Apache Gold
series: Winnetou [1]
And a "second book being a continuation of the first" is surely just another series?
Then with a metadata plugboard your book can appear as "Winnetou 1 - Apache Gold" or formatted however differently you like. And this cover plugin already displays the series name on a separate line so you don't have to do anything special with it.
Personally I won't be making a modification to the plugin to try to split on "dots", there are way too many cases where it would go wrong (Mr. & Dr. etc). However you have the plugin source code, so if you want to make the changes yourself for your own personal usage then go for it (bearing in mind you will have to continually integrate with any future plugin updates). A warning that it is not quite trivial though, there is a lot of "nasty" code to do with sizing things in there which you will have to "break" to compensate for a title taking multiple lines.
