nope , you wont be able to use the lr for another system untill the reading turns out at zero but with time(almost a month depending on the quality of lr)the lr will consume all the amonia and covert it.
if your planning on taking the rock out of the tank that has a high level of amonia and adding it to another tank i would not do that you have to wait for the rock to cycle now.
amonia will kill off alot of the life in the rock but bacteria itself will be fine as long as salinity and temp are stable.flow must be present as well.
heres some reading material on the nitrogen cycle
http://www.reefcorner.com/Manual/nitrogen_cycle.htm
hope this helps