tweaking output with 2.3.x

[J. Scott Amort]

Hi All,

I had asked this question over on lilypond-user, but no answer was
forthcoming (except by Mats, who directed me to this list).  I would
like to tweak the output of a score generated by 2.3.16 - specifically,
I need to vertically move the start and end points of a slur
individually (i.e. not just raise the entire slur by adding some extra-
offset), as well as adjust the arc height (but I think I have that one
figured out using height-limit), and finally, to change the length of a
trill spanner (as well as a hairpin, but I suspect they are the same).
There doesn't seem to be any specific \override or \set commands to do
this.  Is it possible?  If not, may I submit a request for these options
in future versions.  Lilypond produces some very impressive default
output, but there are always cases were items need to be tweaked, and it
would seem that the ones I have mentioned would benefit from an
interface.  Thanks very much.

Best Regards,
Scott