Tom's comments about tuning are very true. The note you can expect an instrument string to produce depends on three factors. The length of the neck, the thickness of the string and how tight you stretch it. If any of the three are significantly different from the instrument the set of strings are sold to fit, you could have problems tuning. Of course it is possible to use a higher or lower gauge string to produce an appropriate tension for the neck length, but the different forces applied to the neck may not do the instrument a lot of good.
To my mind, a mandola has been built to sound right in a specific sound range, so you would not be doing it justice by dropping the tuning. As Les says, playing in CGDA, makes a slight difference to playing in some keys, but for a lot of tunes, you just move the fingering from a mandolin up one string until you run out of strings. For some tunes, you would then have to drop an octave and work out different fingerings. As someone who has played both mandolin and a short necked CGDA tenor banjo, there is a lot of overlap between the two tunings, but each tuning can make playing some tunes simpler and more natural than the fingering used in the other tuning. Alternatively, some tunes work better in one or other tuning.
My advice (if it IS a standard mandola and not an Octave job), would be to give it a proper try in CGDA before trying to re-string for a different tuning.
Quack!
GtD.