No, it is not later BOAC, it is just different. However we do clear all SOPs first with Boeing and then of course with the relevant authority before they are put to use. And yes, the usage of ARM is indeed one of the very few things we still have from the BA heritage as part of our company once was owned and audited by them (same as DODAR, however that we had to abandon in favor of FORDEC after a recent IOSA audit).
From what i can get out of our technicians and our manuals (although the latter do not say much about it) MSR is not available once APR mode has kicked in, however the A/T should provide low speed protection unless you enter RETARD mode because RA1 is below 27ft, in that case there is no more low speed protection (same for ARM operation by the way, low speed protection: yes, MSR: no, low speed protection during RETARD because auf RA1 < 27ft: no).