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>>>>....I'm not a guitarist, but don't many of them play in DADGAD or similar, tuning the low E string to D? In other words, wouldn't they want you do D as well as Eb?...>>>
DADGAD is an alternate tuning. Not the same as capoing. The isea is that the open strings sound different from fretted strings. The first such alternate is DGDGBD. This makes a G major chord on the open strings. It has a very nice resonant, full sound. Banjos and steel guitars use tunings of this kind, but the reason and the usage are a bit more sophistcated than just changing key.
The guitar animation already has options for a number of these alternate tunings. If you can get your hands on a guitar, try them out. Its a lot of fun. Kinda like playing on the black keys.