#1
Once you have a song recorded does some software allow you to change the key without having to re-record everything? I'm using Cubase LE and we our standard tuning is a whole step down. We just recorded a song that we think would sound better only a half step down.
#2
You can use what is referred to as a pitch-shifter, (cubase SHOULD have one) but this will raise EVERYTHING by a semitone, even the drums and vocals, which could put you in what I call chipmunk realm.

That said, depending on the effectiveness of the actual shifter, you may be able to get away with one semitone. Bear in mind that anything more than this is unlikely to sound good.
#3
A pitchshifter, however it WILL sound unnatural and probably not all that great. But sometimes allow you to achieve interesting effects.
#4
Cubase does have one, you just select the desired part, rick click and process>pitch shifter. If you do it too much or too directly, however, it can sound really processed and unnatural, but any excess of effects can produce that.