New try with lyric extender

[Yann]

Hello all :)

I wanted to try again to find a solution to adapt the length of a
lyric extender in order to take into account all voices in a SATB
hymn, as I described sometimes ago in
http://lists.gnu.org/archive/html/lilypond-user/2013-11/msg00810.html
and following messages.

So I read some sections of the learning manual (about modifying
properties and tweaking, which I still don't fully understand). Using
the notation manual and internals reference, I found that lyric
extenders are object of the kind "Lyrics.LyricExtender" . Am I correct
till there ?

Then, I have the following questions :

-Is there a way to display (to console for example) the value of a
given property ?
I tried with #(Lyrics.LyricExtender.minimum-length) or \display
Lyrics.LyricExtender.minimum-length but I don't know where to place
such directive, should it be correct.
-If I'm not mistaken, I should be able to modify the properties of a
single object using for example \once \override
Lyrics.LyricExtender.minimum-length, placed somewhere before the
object I want to modify. Is it correct ?
-If so, is there a way to get the property of a particular single object ?

I've seen that there's a user settable property of the
lyric-extender-interface called "next". How can I access this ? Could
it be of some help for my current problem ?

I'm sorry if my questions look somehow messy, and not rigorous (I may
be confused between different concepts, such as properties,
interfaces...)

Yann