foufymaus,
You can easily splice a length of cord into the foot controller wire. I've done it and works quite safely.
I did this on my Alden ZZ machine for the same reason. Although the wiring was in overall good condition, the controller cord was too short. I just split the old and new cord enough to solder splice it and used heat shrink on each wire then the entire cord at the splice. Put a couple new connectors on the end of the wire for the controller and all is well.
That's a nice machine. I have several of the Japanese machines and they are really quiet. I love the quiet.
Joe