When I lock a hopper after changing the blockdata:

, the tranfercooldown automatically resets to its original transfer rate.

To reproduce:

Make a hopper clock. Make sure hoppers are pointed at each other

Use comparators on each side of clock to see transfer rate:
[C=comparator, H=hopper] "CPPC"

Stand on top of hopper, and use this command:
" /blockdata ~ ~-1 ~

"

• = any number between 0 and 65545

Lock hopper by putting an "on" red-stone signal pointing at it.

Unlock hopper

Make sure to look at the comparators, and see the magic happen!