In case we resurrect this project:
One thing I've already found out is that in 4mm mode you can advance by 2mm.
Press green and holding it down, press yellow and holding it down, release green and the tape get advanced by 2mm.
While still holding yellow down you can press green multiple times.
This, I assume, is to 2mm align the tape in 4mm mode.
Configuring 2mm/4mm mode:
You need to have a tape loaded, so that the yellow LED doesn't flash.
This is the magic trick why I hadn't manged to find this myself, since I'd always tested without tape.
And trust me, I had tried the right combination.
Press green, wait until the shutter closes again and keep holding it down.
Press yellow once for 2mm (twice for 4mm, later tripple lane 8mm feeders can also do 8mm).
The yellow LED should flash once for 2mm, or twice for 4mm.
The feeder has a small I²C EEPROM (X24C44 in my case) to store the configuration.