The ignition lock cylinder has went bad on my prelude. Ive grown up and currently work in the automotive industry. My question is will i have to reprogram the ECU once i replace the lock cylinder kit (comes with immobilizer)

Don't ever ASSUME! you may want to call the dealer and find out. give them your vin# and they can tell you if it's been done,before you go spending $500.00-$800.00 on that switch,depending on where you buy it and if A/T or Manual Transmission,because there are TWO different recalls on the ignition switch.i just sent the recalls to you!

This really doesn't answer my question if i do replace does the ECU have to be reprogrammed

yes,if the key switch is replaced, then the immobilizer system will have to be reprogrammed.

Ok the kit comes with a new immobilizer...but the ECU doesn't have to be reprogrammed