This is probably going to sound a stupid question, and I don't really need an answer (I'm just interested). If you take both an A and a Bb clarinet into an exam (say to do the mozart clarinet concerto on the A and something else on the Bb), can you then choose which instrument you do your scales and other supporting studies on? It doesn't apply to me, but I know people who find it easier to do scales on their A rather than their Bb due to the spacing, and I was just wondering if you could choose. Or is this just a really stupid question?

I'm actually not sure but i should imagine you can do it on either! I did Mozart Clarinet Concerto for my grade 8 on the A, and the rest on the Bb, never actually thought about it!!

The syllabus says

"The syllabus may be offered on a clarinet in Bb or A in any grade"

Yes, I'm sure either would be fine!