Followed these instructions and successfully flashed from 12.5.2 (CN) to 12.5.3 (.EU).
Thanks very much for sharing (and thanks very much to Dev team - ROM is great!)
Has any brave soul had any success with flashing from CN 12.5.2 to Global 12.0.1 as yet (in order to then flash with 12.5.2 EU)?
I noted that ADB Fastboot tool includes an option to disable rollback protection, so it looks like it should be possible, but I've not tried yet.