Indent only one system, replace long extender with dashes

[Frederick Dennis]

Dear All,
\version "2.12.2"
How do you indent just one system?
I've got some shortInstrumentNames appearing at bar
23, the previous bars being hidden, so
short-indent in \layout makes room for the
names, but also indents all the other
systems which I don't want.

Also, the section is voices singing: "Ah".
I used a hidden slur to get an extender
but would rather have a line of dashes
as the extenders look ugly to my mind.
How do I replace a long extender with
a row of dashes?

Thanks for your attention. I have looked in
the docs and the listservs.
Fred.