noise unit,
i dont remember on any of the boeing acft i flew (B744, B772, B734), there's any mention of CLB thrust selection based on TOW. therefore, it lead me to believe generally boeing crew just accept the default CLB-derate associated with the derated-TO thrust. not sure how it's done on the airbus.
"If so, what happens to the CLB derate if reduced TO thrust is selected using ATM?"
not really sure how is it on the airbus but on the boeings, once you have decided your TO derate and Assumed Temp, you enter it into the FMC and the appropriate CLB derate will be selected i.e. CLB, CLB1 or CLB2. If i'm not mistaken, the CLB derate is based on the highest CLB thrust WITHOUT exceeding the selected TO thrust.
we do have a procedure where we manually amend the CLB derate. say for whatever reason you decided to takeoff using Full TO Thrust even when you can use TO derate (usually it's due to poor runway surface or slippery runway). then you find your TO derate and Assumed Temp and enter it in the FMC, check the selected CLB derate. Then, delete the selected derate and Assumed Temp to get Full TO Thrust. By doing so, the CLB thrust will default back to full CLB. we then manually select the required CLB derate.
SR
PS: on the boeings, we have 2 kinds of 'derates'. One is a takeoff derate i.e. TO, TO1, TO2 and the other is Reduced Takeoff using Assumed Temp.
Takeoff Derates is determined by your TOW and selected through FMC. it is as if you put on a smaller engine. therefore, it reduces your Vmca and is recommended for Contaminated Runway. Tafeoff Derates should not be cancelled in an engine failure as it can affect your controllability.
from your derated TO, you can further reduce your TO thrust if weight permits, by entering an Assumed Temp into the FMC. this is called the Reduced Thrust. this reduced thrust can be cancelled and increased to your Derated TO thrust during an engine failure.