In classic country (and to a lesser degree pop), it's quite common for the key to change in the middle of the song. I believe the technical term for this is "modulation." There are a million examples from the world of country music, but a couple that come to mind are George Strait's "Amarillo by Morning" (shifts down a whole step from D to E before the final verse) and George Jones's "A Picture of Me (Without You)" (shifts up a half step from F# to G after the first verse).
Whole-step changes are generally pretty easy to handle on guitar, although it obviously helps to understand the relationships between chords within the major scale. A song that starts in the key of G major and has a I-IV-V progression (G-C-D) can still be played with open chords when you move up a whole step to A major (A-D-E). Thus, to use "Amarillo by Morning" as an example, there's only one barre chord (F#m) when start the song in D, and still only one barre chord (G#m) when you shift down a whole step to E later in the song.
The thing I'm struggling with is half-step key changes, which actually seem to be more common. If a song with a I-IV-V progression starts in G major and then shifts up a half step to G# major, you're suddenly playing G#-C#-D#. Ughhhh. I'm primarily a bassist, and it's super easy to change keys on bass, so this is a new challenge for me as I'm trying to improve at rhythm guitar.
I'm at a point with my playing where I can strum complete barre chords on acoustic guitar for several minutes, but it's obviously not comfortable and they don't ring out like open chords. It's also more difficult to walk between barre chords, and impossible or extremely difficult to do many of the open-chord fills. I'm curious how the professionals handle this issue, both live and in the studio.
I've looked on YouTube for videos of artists playing songs with half-step key-changes, and I've seen a few approaches other than simply playing ordinary barre chords. Two are very simple:
1. Some artists just play the song in a single key live. That's a very easy fix.
2. Some singers with a full band don't start strumming at all until after the key change. This is also an easy fix, but only works if you have another guitarist (or two), or at least a keyboard or pedal steel player.
Two other approaches are more mysterious to me:
3. In some instances, I've seen videos where the capo magically shifts on the neck of the guitar, although I haven't been able to find a video of someone actually moving his or her capo mid-song.
This concert video of George Jones is an example. At 0:09-0:17, the capo is on the first fret. At around 0:50, the key moves up a half step, and you can briefly see Jones turn his guitar body up towards the ceiling. Then the video cuts away, and the next time you see the neck of his guitar, at around 1:20, the capo is up on the second fret. I assume when Jones turned up the body he was preparing to move the capo up one fret, but I've tried doing that myself and it's very hard to do smoothly between verses. Maybe it's just an acquired skill? Either that, or it's something that only works when you're in front of a full band (like Jones) and nobody will miss the rhythm guitar for a few beats.
4. Finally, I've seen some people play what look like partial barre chords up the neck. Some of these look like moveable C-shape chords, where you don't have to bar the entire neck, but I've had trouble identifying others. The moveable C-shape chord obviously doesn't sound like an open chord, but it's a bit easier for me to play a "partial" D# up the neck using the C shape than a "full" D# barre chord with the standard A shape.
So here's my question:
How do you handle these half-step key changes? Do you play full barre chords? Modified or "partial" barre chords? Quickly move the capo up or down a fret? Play the song in a single key?
I've been trying to solve this problem on my own for a while, so any input would be appreciated!