No, allowBeamBreak does exactly what it says, namely allows line breaks
in the middle of a beam. Example:
\relative c'{c2. c8 [ c \break c c ] c2. }
it has nothing to do with breaking lines in the middle of the duration
of a note. Why not try a small test case before
you send these corrections?
Please test a suggestion before sending it. The below code does not
produce a line break at the first line break, which is what the info in
the documentation warns about.
{
\set Score.allowBeamBreak = ##t
c4 c2 c2 \break % this does nothing
c2 c4 | % a break here would work
c4
http://lilypond.org/doc/v2.8/Documentation/user/lilypond/Line-breaking.html#Line-breaking
This page lists a bug stating:
Line breaks can only occur if there is a “proper” bar line.
A note which is hanging over a bar line is not
proper, such as
c4 c2 c2 \break % this does nothing
