I think it can be done as my own BCM 50 system has recently been modified to have the latest Avaya firmware (*.C91) files put it in.
-rwxr-xr-x 1 root root 2087229 Nov 13 13:17 0602B76.bin
-rwxr-xr-x 1 root root 2087261 Nov 13 13:17 0603B76.bin
-rwxr-xr-x 1 root root 1755691 Dec 29 2014 0604DCN.bin
-rw-r--r-- 1 root root 3934497 Nov 13 13:18 0621C91.bin
-rw-r--r-- 1 root root 2696657 Nov 13 13:19 0623C91.bin
-rw-r--r-- 1 root root 3359305 Nov 13 13:19 0624C91.bin
-rw-r--r-- 1 root root 3701069 Nov 13 13:20 0625C91.bin
-rw-r--r-- 1 root root 4161717 Nov 13 13:20 0626C91.bin
-rw-r--r-- 1 root root 3602249 Nov 13 13:21 0627C91.bin
-rw-r--r-- 1 root root 3538761 Nov 13 13:22 062AC91.bin
-rw-r--r-- 1 root root 2945330 Nov 13 13:22 2310S99.bin
IpTerminalFirmware.bcf
-rw-r--r-- 1 root root 4660617 Nov 13 13:23 SIP1120e04.04.23.00.bin
-rw-r--r-- 1 root root 4840097 Nov 13 13:24 SIP1140e04.04.23.00.bin
-rw-r--r-- 1 root root 5172473 Nov 13 13:25 SIP1165e04.04.23.00.bin
-rw-r--r-- 1 root root 4446701 Nov 13 13:23 SIP12x004.04.23.00.bin
My 1140e phone upgraded to the latest bin file without any problems.
Firebird Scrambler
Nortel Meridian 1 / Succession and BCM / Norstar Programmer in the UK
Advance knowledge on BCM support