I'm learning the song 'let it be' by the beatles in the key of C however, It's just a tad to high for me (The highest note that is). The key of A, or even B work completley fine and I could capo that and change the chords very easily - But I've learned an extremely complicated fingerstyle piece/chord progression and a solo as well. I was wondering if I can use a drop tuning and capo placement to drop the key of the song down a tone or two so that they key of the song will change but not the chord shapes, (essentially a reverse capo) so all the practice I did on the guitar won't go to waste.
You can make use of drop tuning. This is a very popular method used by rock and metal bands to accomodate the vocal range of the singer.
This also accomodates the guitar player. By dropping your tuning of your guitar, you not just lowering the key, but you get to retain all the original chordshapes. What this means is, if a song is written the key of C, and you hold an C chord, in standard tuning, the sound will be that of a C chord. If you drop your guitar one half step down (Eb,Ab,Db,Gb,Bb,eb), you drop the key of the song to B, and if you hold and strum the C chord as before, you will now instead hear a B chord, and not a C.
So you see that, instead of having to play the dreaded B chord as a major barre chord in normal tuning in order to drop the key of the song one half step, you drop your guitar's tuning half a step and you still play the C major chord shape as before, which is more finger friendly
I just thought of this now, and is just a nice-to-know. If you need to tune down your guitar, and only have a cheap electronic tuner like me which can basically just tune standard tuning, make use of your capo.
What I always do is, say you need to tune down half a step, just place your capo on the first fret, then tune your guitar to standard tuning using your tuner. Once that is done, and you remove the capo, your guitar will be tuned down half a step. For a full step drop, place the capo on fret two, for one and a half step, use fret three and so on
You can also use a harmonizer pedal like a Digitech Richochet to drop everything you play a certain interval. It has a latch mode that you can simply always leave on.
As others have mentioned, drop tuning by up to one whole step is a viable solution. However if you only use the half to one step flat tuning for that particular song, it might not be convenient to re-tune the guitar after playing that one song.
If you drop the tuning one whole step flat from standard, you might benefit from some adjustments to the set up. The lower string tension may contribute to some fret buzz if your action is low. An adjustment to the truss rod and/or saddle height and corresponding tweaking of the intonation would compensate for the slack strings. Another solution is to use heavier strings which may tune flat with close to the same tension as the lighter strings on standard tuning.
For all these reasons, it might make sense to invest in a second guitar to leave tuned flat for the songs that require it. Then you can have the string set and set up optimized for the drop tuning.
But if you are going to spend the money on a second guitar, as long as you play a solid body electric guitar, you could just as easily use a pedal such as the one mentioned by Neil Meyer or the less expensive Digitech Drop pictured below. The DigiTech Drop provides anywhere from 1 to seven semitones of polyphonic down tuning plus a whole octave down.
Finally, (not as an answer to your question but as an aside) I play Let It Be on guitar using the chord set from the key of G and have also found some nice licks and fills that are easy to play. By putting a capo on the second fret I am playing the G chord set but the tonality is in the key of A. If you want to try it with the G chord set the chords are G D Em and D. I use a D with F# bass in the chorus and at the end of the chorus I play a C (Bm Am G) walk down. Leave a comment if you want the chord progression for the prelude to the solo.
Good luck and have fun.
Just as you suggest, you could drop all the strings one tone to DGCFAD. Or if you can manage to fret that high, you could capo at the 10th fret to drop the tonality by one tone. The capo option will be easier with a cutaway.