Trying to use ly:grob-set-property!

[Kevin Barry]

Hi Lilypond users,

I am trying to get something to work by setting the X-offset of a grob
using ly:grob-set-property but I must be doing something wrong,
because it seems to have no effect. Can anyone explain what I'm doing
wrong? Below is a minimal example showing what I mean.

%%%
\version "2.19.84"
{
  \override TextScript.X-offset = 10
  c' ^"this is offset"
}
{
  \override TextScript.after-line-breaking =
  #(lambda (grob)
     (ly:grob-set-property! grob 'X-offset 10))
  c' ^"this isn't offset"
}
%%%

Thanks in advance,
Kevin Barry