For certain pieces, especially some lute transcriptions, Segovia and other classic guitarist will tune the 6th string down to D. For some lute pieces, I've seen classic guitarists occasionally tune the 3rd string down a half-step so they can play the piece with the same fingering a lutenist would use. I also know a lute-player or two who tune the top six courses of their lutes exactly like a guitar (that involves tuning the 3rd string up a half-step). But a classic guitarist retuning more than one string is extremely rare. Usually a classic guitarist is playing from written music, and most classic guitar pieces are written in (or if transcribed from another instrument, transposed to) keys that are relatively easy on the guitar. Stringed instruments are usually easier to play in sharp keys, wind instruments easier in flat keys (in an orchestra, somebody's gotta give).

An accompanying instrument should accommodate the voice. If you must absolutely sing a song in Eb and either D or E won't do, use a capo. If you can only get the kind of accompaniment you want with certain chord forms, say A, but you want to sing the song in C, then capo up three frets and use the A chord forms. The song is what's important here. A capo is a very useful tool, and it's foolish not to use one if it accomplishes the purpose. The only time that a capo becomes a "cowboy's crutch" is when a person wants to learn only one or two keys and use the capo for everything else. That's just lazy, and the person misses a lot of great possibilities.

One reason we know that Segovia never used a capo is that hell hasn't frozen over yet.

Don Firth