[JonPR]

Originally Posted by morningside

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)

That's what we musos call "up" a whole step.

Originally Posted by morningside

and George Jones's "A Picture of Me (Without You)" (shifts up a half step from F# to G after the first verse).

There you go.

Originally Posted by morningside

The thing I'm struggling with is half-step key changes, which actually seem to be more common.

In certain kinds of song, yes.
The popular term for them is "the truck driver's gear shift", because of their shameless crudity. https://tvtropes.org/pmwiki/pmwiki.p...versGearChange
It normally sounds like the singer (or composer) thinks the song is getting boring at this point, but it's too short to just stop there, and the composer couldn't be bothered to write any more. So, to keep going, it needs an injection of energy, and the obvious way to do that is just kick it up a half-step - yee-hah!
Some songs do it more than once. My favourite for its reckless bravado, its sheer chutzpah, is Bobby Darin's Mack The Knife - https://www.youtube.com/watch?v=h8iPUK0AGRo - five truck driver changes in less than three minutes. Respect due!

Originally Posted by morningside

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.

You just have to get used to barre chords, but also remember you don't need to play all 6 strings on every chord. Partial chords (with some strings muted) can work fine. There are movable shapes (no open strings) which are not barres.

Originally Posted by morningside

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.

Here you go. https://youtu.be/c80pa9lCFjQ?t=77
The time stamp skips the lengthy intro where he explains that it was written as a show-off piece in the 1960s, to impress the beginner guitarists in the audience. I remember (as one of those beginners myself) seeing him perform it in 1968 and nearly fell off my chair when he moved the capo. (Keep watching, he does it 3 or 4 times, and then detunes his 1st string. His tuning is DADDAD, btw.)

He's using a simple elastic capo there, but now you can get roller capos designed to be movable mid-song. However, I bought a roller capo for this purpose and it doesn't work too well - it tends to roll the outer strings off the fretboard, at least it does on my guitar. YMMV - bargain here: https://www.amazon.co.uk/Adjustable-...N5K/ref=sr_1_6