Change stem direction for voice?

[Stefano Antonelli]

Hello List,

Is it possible to change the stem direction for an entire voice from a
context?  Something like this doesn't work:

\layout {
  \context Voice = "voiceTwo" {
    \override Stem.direction = #UP
    \override Slur.direction = #DOWN
    \override Beam #'positions = #'(5 . 5)
  }
}

The Beam position appears to work, but not the stem or slur directions.
 I read somewhere that:

\stemUp expands to \override Stem.direction = #UP

So that's why I'm using it.

I'm also experimenting with voiceTwo because it defaults to stems down.
 And I'd like voiceTwo to be stems up.

If it can't be done through contexts, is there any way to force stem
directions for a given voice without adding \stemUp or \stemDown to the
notes themselves?

Thanks,
Stef