Well, in the first place JSF is a Web UI framework. So, anything that you expect to output to the user will end as HTML (with the only exception of javascript, though). So, I don't find it a grave violation of MVC (if any at all). Maybe you could even push the envelope and directly use <br/>
inside the text, instead of replacing \n
In a more general sense, if you have different lines/paragraphs in your text, the more flexible/standard solution would be break your text in the different elements and let your presentation logic handle it. So, instead of a properties with
presentationPage.introductionText=Ipse Lorum ...sum.\nVini vidi vinci.
You would end with
presentationPage.introductionText.par1=Ipse Lorum ...sum.
presentationPage.introductionText.par2=vini vidi vinci.