Redefine r? Horizontal beams? Grace without beam break?

[Hugo Flordal]

Hi, I'm using Lilypond 2.10.25 and I have a few questions...

  Is it possible to redefine the "rest note name" 'r' and instead use e.g. 'p'
for rests. I'd really like to use 'r' for something else (right hand strokes in
drumming).

  Can you have _really_ horizontal beams (possibly always at the same hight)?
The following line does not work, the beams are still leaning ever so 
slightly...
\override Beam #'damping = #10000000

  Another thing, how would I tweak the automatic beaming to have grace notes
that do not "break beams"? For instance, I'd like the first code snippet to
produce the same output as the second.

  \stemDown
  a8 \grace {c16[c]} a8

  \stemDown
  a8[ \grace {c16[c]} a8]


 thanks!
   hguo