rd> I would imagine that a new version of the Texinfo tools will
> trickle down only after a few years.
FWIW, you can download the current (released) texinfo.tex from
https://ftp.gnu.org/gnu/texinfo/texinfo.tex and, as Gavin says, put it
in the document directory. texinfo.tex is a standalone file.
Users can use a particular version of texinfo.tex by placing the file
in the directory with the Texinfo source files.
Untested, but it should also be possible to override texinfo.tex macros
with an @tex block in the document, e.g., to allow more stretch in this
particular document:
@tex
\global\def\urefallowbreak{%
\penalty0\relax
\hskip 0pt plus 4 em\relax
\penalty1000\relax
\hskip 0pt plus -4 em\relax
}
@end tex
karl
