Okay, I was able to get this phone successfully downgraded from Avaya IP Office SIP firmware version 12x0.01.01.04.00 to UNISTIM firmware version 062AC8Q.
At first, trying to get the phone to upgrade during the firmware check at software load would not work. It kept asking for an .xml file that I could not provide.
My next attempt was to use the in-program upgrade function to attempt to get the phone to load the UNISTIM firmware. I could get the phone to connect to my TFTP server and grab the 1230.cfg file (that's the file it was calling for,) but the phone would error out saying "no upgrade required."
So here's what I did:
1. Since I knew that the phone's firmware was looking for another newer version of SIP firmware, I went ahead and looked online at Avaya's website for the most recent version of SIP firmware available for the 1230. Downloading that firmware gave me a file named "SIP12x004.04.10.00.bin." Okay, so that's the newer file name. What if I trick the phone and rename my UNISTIM firmware to that file name and update my 1230.cfg file?
2. So that's what I did. I made a copy of my 062AC8Q.bin UNISTIM firmware file and called it "SIP12x004.04.10.00.bin." I placed my "cloaked" firmware file in my TFTP root folder and modified my 1230.cfg file as such:
[FW]
DOWNLOAD_MODE FORCED
VERSION SIP12x004.04.10.00
FILENAME SIP12x004.04.10.00.bin
PROTOCOL TFTP
SERVER_IP 204.224.107.188
SECURITY_MODE 0
3. Then I used the in-program upgrade option to attempt a phone software upgrade. The phone pulled in the 1230.cfg file, noted the newer firmware version, and immediately threw the phone into BootC mode. SUCCESS! Now we're getting somewhere.
4. Once in BootC mode, the phone would not finish programming. Looking at my TFTP log, I noticed the error message "TFTP error from 204.224.107.191 requesting 12xxBoot.cfg : File does not exist" Aha....now that the phone is in BootC mode, it's looking for instructions found in a .cfg file called 12xxBoot.cfg. Okay, let's make one. So I opened up Notepad, and created a 12xxBoot.cfg file the following contents:
[FW]
DOWNLOAD_MODE FORCED
VERSION 062AC8Q
FILENAME 062AC8Q.bin
5. I made sure I had a copy of my 062AC8Q.bin firmware in my TFTP root folder, and the next time the phone rebooted, it grabbed the new firmware file and swapped it out, turning the phone back into a UNISTIM flashed phone.
Whew! That was a weird one.
So, in short:
1. Trick your SIP phone into BootC mode by "cloaking" your UNISTIM firmware into a name the SIP program will understand as "newer firmware."
2. Once in BootC mode, program your 1230 by using the 12xxBoot.cfg file. Insert UNISTIM firmware of your choice.
Hope this info helps someone else in the future.