TextSpanner: Change text at automatic line break?

[James Harkins]

Hi,

Using a TextSpanner, is there a way to change the text in the middle, so that 
the new text appears at the next system break (whichever bar that is)?

\version "2.19.80"
\language "english"

\relative c' {
  \override TextSpanner.bound-details.left.text = "abc"
  c1 \startTextSpan
  \repeat unfold 20 { c1 }
  c1\stopTextSpan
}

With default settings, LP engraves 11 bars on the first line, putting bar 12 on 
the next. I know I could stop the spanner at the end of bar 11 and start a new 
one on bar 12, but future changes might move the line breaks, so I would rather 
not have to hardcode. I would like to set some property in the middle of the 
spanner and have it take effect at the next automatic system break.

I tried overriding TextSpanner.bound-details.left.text -- no difference on the 
second line.

Same for TextSpanner.bound-details.left-broken.text -- if "left-broken" has a 
text property, it's ignored for rendering.

If it's too hard, I can change the notation style. (It's a score for computer 
ensemble. The text indicates which patch and which variant to play. The variant 
might change in the middle. I'd like the text to change accordingly. If it 
isn't possible, I'll use the spanner only for the patch name, and put the 
variant underneath.)

Thanks,
James