An UPDATE
1. I spoke to the COM in the DO I would transfer to. They had a space for me and wanted to do it ASAP. Agreed the 6 month min was the state of play.
2. Spoke to COM in my DO, who restated the 1 year limit but climbed down immediately when shown evidence. Agreed to let me go.
3. CoM in target DO asked for my Employee ID number to make the transfer. Start in a couple of weeks.
The old way of sucess factors and transfer lists doesn't seem to apply any more. Frontline jobs do not get added to sucess factors. And afaict, there is no transfer list process - asked union rep about this, who asked higher up but couldn't find out anything helpful.
If you don't know the manger in the DO, you can use the organisational structure page on Sucess Factors to identify them and send an email or make a call if their number is in their profile.
TLDR: speak to the DO manager you want transfer to start with. Then, if there is an option to transfer, talk to your current COM.