I just stumbled over the following "problem" when creating a presentation with
Impress and I haven't found any other issue on this I thought I submit this here : 

Objects in Impress seem to be organized in two different groups : graphics
styles and presentation objects (with the corresponding styles). In brief : As
far as I can see (using help and trial and error) there is no way to convert a
graphics style into an presentation style.
Why would I want to do that ?
It seems to me that presentation objects can only be created by selection a
"Layout" and then using them.
However when I want to begin with an empty slide and then add some text objects,
there seems to be no way (at least not one I easily found or was described in
the help) to say later on "This text box is a Title" or "this text box is an
Outline", using presentation styles.
This concerns mainly the text box.
What's the difference between a text box created using "Layouts" and containing
an outline, and a text box inserted using the "text" button, containing an
outline, to require two different types of styles. If I then change the style of
the presentation style outline, the other one will not be changed.
This is very confusing for the user, especially for titles and outlines

Thanks to have listened (read :-)

Oliver