I wonder if on-house procedures are approved by boeing? If not, what will you do in case of an accident? The manufacturer can not be held accountant for something if you don't follow it's procedures.
Regarding ARM use for the a/t , you'll have a "nice" surprise if landing low weight,on a gusty wind...high thrust set by the a/t just during flare,as it senses the approach to stall (low speed,momentary high AOA) . It has happened before ,it will happen again, and we'll talk then about your view of using the a/t in ARM.
The Bus is different in design of the autothrust, so don't try to duplicate it.
Also, on the Ng there is nothing to worry,you may firewall the throttles ,no problem..
My 2p,do as the manufacturer says..it has test pilots and engineers to create its procedures.