Thanks for your input, Joe!
I just went ahead and did it. I'm very happy with the result.
I'll just post a quick illustrated rundown if somebody else wants to do the same thing.

Mark a line right below the words. That's the place to cut it!
Make sure to wear eye protection and a dust mask (!), you don't want to breathe aluminium sawdust!

After cutting it with a Dremel tool.

Check how the yellow top part of the enclosure fits and mark the place where to cut.

When cutting metal I think it's good to have some sort of coolant. I use water. This also makes for less airborne sawdust.

Trim the PCB to make the lid close. (Note how they crammed in the PCB and misaligned the holes for the pots

)
Again: Dust mask!

In this image I've already drilled the new holes for the screws that hold the to halves together.
Since the housing comes pretty close to the main socket I thought it's better to be safe and have some insulation in case something goes wrong.
Triple check all the insulation of the mains wiring before putting everything back together! Also check for scrap metal or sawdust inside the box.
Take of the rubber feet.
Here's the final thing. It just barely fits under the Pedaltrain Pro without any further modification of the pedal board.




If you look closely you'll see that I didn't saw off the rear yellow overshoot... I wanted to, but my dremel crapped out on me.
So I just took of what was necessary with a file. Could've done a nicer job but who cares. The thing will spend its days under the pedalboard anyway!
When I'm done mounting it to my new board I can post a final image.
Woohoo! Just saved myself a hundred bucks!
