Hi Yvo,
I think the best way is the position of the bricklet. So you have to plug the bricklets to the same positions and you can identify them with the enumeration callback.
It is also possible to override the UID with the Brick Viewer, but for this you have to connect each bricklet and override the UID.
I think first way is better because hardware is like it is. It is more plug and play (work) :)
Greets
Chris