We have asked about that, and they say its not possible.
The bore caps are 20mm and 25mm respectively, so you cannot swap it across unfortunately.
There is a specific tool required to swap the caps over, we currently have one and can do the job if required.
And as Danny says, we have the brake in 180mm version (not seen it anywhere else, actually), so no need for extra adaptors.
I think thats all... anything else, just shout (Y)
Cheers,
Adam