From the API documentation :
Specify acceleration data for current geometry. Input acceleration data should be result of rtuTraversalGetAccelData or rtAccelerationGetData call.
From what I understood, what this could do to help you is to provide a way to keep your accelerating structure somewhere and to reload it whithout re-building it when needed.
So tha data parameter should be set to a pointer to the memory space containing your accelerating structure.
For example, after setting an accelerating structure accel, you could do that :
void * data = malloc(data_size);
Which would store your acceleration structure in memory space data.
And after, when you’d need to reload it :
RTacceleration new_accel; // Which won't be built but set.
rtAccelerationSetData(new_accel, data, data_size);
If your memory space is not altered, that should give you the same acceleration structure as before.
The procedure should be the same pour traversal data.
I hope it helps.