Is chromosomal crossover considered a mutation? Would this be a large-scale mutation?
There are many different ways a DNA sequence can change. Labeling a change as a mutation implies that there was a biological process in which DNA was damaged then not properly repaired.
Crossing over during the formation of gametes does not result in a mutation.
Crossing over during repair of a double stranded DNA break does result in a mutation.
Yes. And it is especially considered a large-scale mutation when compared to point mutations which effect single bases.